Atrium is an open-source multiplatform assertion library for Kotlin with support for JVM, JS and Android. It is designed to support multiple APIs, different error reporting styles and Internationalization (i18n). The project was inspired by AssertJ at first but moved on and provides now more flexibility, features and hints to its users (so to you
Atrium is designed to be extensible as well as configurable and allows you to extend it with your own assertion functions, customise reporting or even replace core components with your own implementation in an easy way.
Atrium currently provides two API Styles: pure fluent and infix where both of them have their design focus on usability in conjunction with code completion functionality provided by your IDE. See Examples below to get a feel for how you could benefit from Atrium.
Table of Content
- Installation
- Examples
- Third-party Extensions
- How is Atrium different from other Assertion Libraries
- Write own Assertion Functions
- Use own Expectation Verb
- Internationalization
- API Styles
- Java Interoperability
- KDoc - Code Documentation
- Known Limitations
- FAQ
- Roadmap
- Contributors and contribute
- Sponsors
- License
Installation
JVM
Atrium is linked to mavenCentral, jcenter but can also be retrieved directly from bintray.
gradle:
buildscript {
ext { atrium_version='0.16.0' }
}
repositories {
mavenCentral()
}
dependencies {
testImplementation "ch.tutteli.atrium:atrium-fluent-en_GB:$atrium_version"
}
We have defined a dependency to the bundle atrium-fluent-en_GB in the above example which provides a pure fluent API (in en_GB) for the JVM platform.
Have a look at the JVM sample projects for a quick setup, or Maven sample project if you prefer Maven to Gradle.
We currently provide the following extensions for the JVM platform:
- kotlin_1_3: assertion functions for Kotlin 1.3 specific types (e.g. for Result).
You can enable them as follows:
dependencies {
testImplementation "ch.tutteli.atrium:atrium-api-fluent-en_GB-kotlin_1_3:$atrium_version"
}
Also take a look at Third-party Extensions which might come in handy as well.
click to see how the setup for the infix API looks like
buildscript {
ext { atrium_version='0.16.0' }
}
repositories {
mavenCentral()
}
dependencies {
testImplementation "ch.tutteli.atrium:atrium-infix-en_GB:$atrium_version"
}
And for the aforementioned extensions:
dependencies {
testImplementation "ch.tutteli.atrium:atrium-api-infix-en_GB-kotlin_1_3:$atrium_version"
}
maven:
Because maven is a bit more verbose than gradle, the example is not listed here but a sample maven project is provided which shows all necessary setup.
That is all, you are all set. Jump to Examples which shows how to use Atrium.
JS
buildscript {
ext { atrium_version='0.16.0' }
}
repositories {
mavenCentral()
}
dependencies {
testImplementation("ch.tutteli.atrium:atrium-fluent-en_GB-js:$atrium_version")
}
We have defined a dependency to the bundle atrium-fluent-en_GB-js in the above example which provides a pure fluent API (in en_GB) for the JS platform.
Have a look at the JS sample projects for a quick setup.
Otherwise, you need to setup an explicit dependency on atrium-fluent-en_GB-js in your test code in order that you can use Atrium. This is due to the loosely coupled design of Atrium and dead code elimination performed by the Kotlin compiler for JS.
Atrium itself is using mocha as well (see build.gradle -> createJsTestTask) and has tests written in JS modules (see AdjustStackTest) as well as tests written in common modules (e.g. SmokeTest) which are executed on the JS platform as well (actually on all platforms -> JVM uses JUnit for this purpose, see build.gradle -> useJupiter).
We currently provide the following extensions for the JS platform:
- kotlin_1_3: assertion functions for Kotlin 1.3 specific types (e.g. for Result).
You can enable them as follows:
dependencies {
testImplementation "ch.tutteli.atrium:atrium-api-fluent-en_GB-kotlin_1_3-js:$atrium_version"
}
click to see how the setup for the infix API looks like
buildscript {
ext { atrium_version='0.16.0' }
}
repositories {
mavenCentral()
}
dependencies {
testImplementation "ch.tutteli.atrium:atrium-infix-en_GB-js:$atrium_version"
}
and for the aforementioned extensions:
dependencies {
testImplementation "ch.tutteli.atrium:atrium-api-infix-en_GB-kotlin_1_3-js:$atrium_version"
}
That is all, you are all set. Jump to Examples which shows how to use Atrium.
Android
Starting with 0.12.0 we no longer deliver a dedicated -android jar. Instead you can use the same setup as shown in JVM setup. We start adding one again in case we have Android specific assertion functions.
Also take a look at Third-party Extensions which might come in handy as well.
Common
The setup for using Atrium in a common module of a multiplatform project is basically the same as for the JVM setup, you only need to suffix the dependency with -common in addition. For instance atrium-fluent-en_GB-common instead of atrium-fluent-en_GB.
Have a look at JVM, JS or Android to see how the setup of a specific platform has to be done. You might want to have a look at the Multiplatform sample project as well for a quick setup.
Examples
We are using the API provided by the bundle module atrium-fluent-en_GB in the following examples. It provides a pure fluent API for the JVM platform. Have a look at apis/differences.md to see how the infix API looks like, how they differ respectively.
Your First Assertion
We start off with a simple example:
import ch.tutteli.atrium.api.fluent.en_GB.*
import ch.tutteli.atrium.api.verbs.expect
val x = 10
expect(x).toEqual(9)
expected that subject: 10 (kotlin.Int <1234789>)
◆ equals: 9 (kotlin.Int <1234789>)
The statement can be read as "I expect, x to be nine" where an equality check is used (for an identity check, you have to use toBeTheSameInstace). Since this is false, an AssertionError is thrown with a corresponding message as shown in the Output where ◆ ... represents a single assertion for the subject (10 in the above example) of the assertion. In this sense the report can be read as I expected that the subject of the assertion, which is 10, equals 9 -- and needless to say, this assertion is wrong and thus the thrown error.
We are using the bundle atrium-fluent-en_GB and the predefined expectation verb expect in the examples. Thus, the corresponding imports at the beginning of the file in the above example. We will omit the import statements in the remaining examples for brevity.
You want to run the examples yourself? Have a look at the Installation section which explains how to set up a dependency to Atrium.
The next section shows how you can define multiple assertions for the same subject.
Define Single Assertions or Assertion Groups
// two single assertions, only first evaluated
expect(4 + 6).toBeLessThan(5).toBeGreaterThan(10)
expected that subject: 10 (kotlin.Int <1234789>)
◆ is less than: 5 (kotlin.Int <1234789>)
Atrium allows you to chain assertions or in other words you only need to write the expect(...) part once and can make several single assertions for the same subject. The expression which determines the subject of the assertion (4 + 6 in the above example) is evaluated only once.
In this sense we could have written it also as follows (which is only the same because 4 + 6 does not have side effects).
expect(4 + 6).toBeLessThan(5)
expect(4 + 6).toBeGreaterThan(10)
Correspondingly, the first expect statement (which does not hold) throws an AssertionError. In the above example, toBeLessThan(5) is already wrong and thus toBeGreaterThan(10) was not evaluated at all and correspondingly not reported.
If you want that both assertions are evaluated together, then use the assertion group syntax as follows:
// assertion group with two assertions, both evaluated
expect(4 + 6) {
toBeLessThan(5)
toBeGreaterThan(10)
}
expected that subject: 10 (kotlin.Int <1234789>)
◆ is less than: 5 (kotlin.Int <1234789>)
◆ is greater than: 10 (kotlin.Int <1234789>)
An assertion group throws an AssertionError at the end of its block; hence reports that both assertions do not hold. The reporting can be read as I expected that the subject of the assertion, which is 10, is less than 5 and is greater than 10
You can use and as filling element between single assertions and assertion group blocks:
expect(5).toBeGreaterThan(2).and.toBeLessThan(10)
expect(5) {
// ...
} and { // if the previous block fails, then this one is not evaluated
// ...
}
Expect an Exception
expect {
// this block does something but eventually...
throw IllegalArgumentException("name is empty")
}.toThrow<IllegalStateException>()
expected that subject: () -> kotlin.Nothing (readme.examples.MostExamplesSpec$1$7$1 <1234789>)
◆ ▶ thrown exception when called: java.lang.IllegalArgumentException
◾ is instance of type: IllegalStateException (java.lang.IllegalStateException)
ℹ Properties of the unexpected IllegalArgumentException
» message: "name is empty" <1234789>
» stacktrace:
⚬ readme.examples.MostExamplesSpec$1$7$1.invoke(MostExamplesSpec.kt:67)
⚬ readme.examples.MostExamplesSpec$1$7$1.invoke(MostExamplesSpec.kt:22)
⚬ readme.examples.MostExamplesSpec$1$7.invoke(MostExamplesSpec.kt:272)
⚬ readme.examples.MostExamplesSpec$1$7.invoke(MostExamplesSpec.kt:22)
You can also pass a lambda to expect and then use toThrow to make the assertion that invoking the lambda throws a certain exception (IllegalStateException in the example above).
As with all narrowing functions, there are two overloads:
- the first is parameterless and turns only the subject into the expected type; failing to do so cannot include additional information in error reporting though.
- the second expects an
assertionCreator-lambda in which you can define sub-assertions. AnassertionCreator-lambda has always the semantic of an assertion group block. It has also the benefit, that Atrium can provide those sub-assertions in error reporting, showing some additional context in case of a failure.
The following example uses the first overload
expect {
throw IllegalArgumentException()
}.toThrow<IllegalArgumentException>().message.toStartWith("firstName")
expected that subject: () -> kotlin.Nothing (readme.examples.MostExamplesSpec$1$8$1 <1234789>)
◆ ▶ thrown exception when called: java.lang.IllegalArgumentException
◾ ▶ message: null
◾ is instance of type: String (kotlin.String) -- Class: java.lang.String
And this one uses the second overload; notice the difference in reporting.
expect {
throw IllegalArgumentException()
}.toThrow<IllegalArgumentException> {
message { toStartWith("firstName") }
}
expected that subject: () -> kotlin.Nothing (readme.examples.MostExamplesSpec$1$9$1 <1234789>)
◆ ▶ thrown exception when called: java.lang.IllegalArgumentException
◾ ▶ message: null
◾ is instance of type: String (kotlin.String) -- Class: java.lang.String
» starts with: "firstName" <1234789>
As side notice, message is a shortcut for feature(Throwable::message).notToBeNull, which creates a feature assertion (see next section) about Throwable::message.
There is also the counterpart to toThrow named notToThrow:
expect {
// this block does something but eventually...
throw IllegalArgumentException("name is empty", RuntimeException("a cause"))
}.notToThrow()
expected that subject: () -> kotlin.Nothing (readme.examples.MostExamplesSpec$1$10$1 <1234789>)
◆ ▶ invoke(): ❗❗ threw java.lang.IllegalArgumentException
ℹ Properties of the unexpected IllegalArgumentException
» message: "name is empty" <1234789>
» stacktrace:
⚬ readme.examples.MostExamplesSpec$1$10$1.invoke(MostExamplesSpec.kt:88)
⚬ readme.examples.MostExamplesSpec$1$10$1.invoke(MostExamplesSpec.kt:22)
⚬ readme.examples.MostExamplesSpec$1$10.invoke(MostExamplesSpec.kt:89)
⚬ readme.examples.MostExamplesSpec$1$10.invoke(MostExamplesSpec.kt:22)
» cause: java.lang.RuntimeException
» message: "a cause" <1234789>
» stacktrace:
⚬ readme.examples.MostExamplesSpec$1$10$1.invoke(MostExamplesSpec.kt:88)
Notice that stacks are filtered so that you only see what is of interest. Filtering can be configured via ReporterBuilder by choosing an appropriate AtriumErrorAdjuster. Stack frames of Atrium and of test runners (Spek, Kotlintest and JUnit for JVM, mocha and jasmine for JS) are excluded per default. Create a Feature Request in case you use a different runner, we can add yours to the list as well.
Feature Assertions
Many times you are only interested in certain features of the subject and want to make assertions about them.
There are different use cases for feature assertions. We will start of with properties and method calls and go on with more complicated scenarios.
Property and Methods
We are using the data class Person in the following examples:
data class Person(val firstName: String, val lastName: String, val isStudent: Boolean) {
fun fullName() = "$firstName $lastName"
fun nickname(includeLastName: Boolean) = when (includeLastName) {
false -> "Mr. $firstName"
true -> "$firstName aka. $lastName"
}
}
val myPerson = Person("Robert", "Stoll", false)
The simplest way of defining assertions for a property of an instance or for the return value of a method call is by using the extension method its.
expect(myPerson)
.its({ isStudent }) { toEqual(true) } // fails, subject still Person afterwards
.its { fullName() } // not evaluated anymore, subject String afterwards
.toStartWith("rob") // not evaluated anymore
expected that subject: Person(firstName=Robert, lastName=Stoll, isStudent=false) (readme.examples.FeatureExtractorSpec$1$Person <1234789>)
◆ ▶ its.definedIn(FeatureExtractorSpec.kt:43): false
◾ equals: true
In the above example we created two assertions, one for the property isStudent of myPerson and a second one for the return value of calling fullName() on myPerson. A feature assertion is indicated as follows in reporting: It starts with a ▶ followed by the feature's description and its actual value. So the above output can be read as
I expected that the subject of the assertion, which is actually the Person(...), respectively its property which was defined in FeatureExtractorSpec.kt on line 43, which is actually
false, equalstrue.
The second feature is not shown in reporting as the first already failed and we have chosen to use single assertions which have fail-fast semantic.
Feature assertions follow the common pattern of having two overloads:
-
the first expects only the extractor-lambda. This overload narrows the subject to the feature, meaning a subsequent call in the fluent chain is about the feature and not the previous subject.
-
the second expects an
assertionCreator-lambda in addition, in which you can define sub-assertions for the feature. AnassertionCreator-lambda has always the semantic of an assertion group block or in other words, not-fail fast. It has also the benefit, that Atrium can provide those sub-assertions in error reporting, Moreover, the subject stays the same so that subsequent calls are still about the same subject.expect(myPerson) { // forms an assertion group block its({ firstName }) { // forms an assertion group block toStartWith("Pe") // fails toEndWith("er") // is evaluated nonetheless } // fails as a whole // still evaluated, as it is in outer assertion group block its { lastName }.toEqual("Dummy") }
expected that subject: Person(firstName=Robert, lastName=Stoll, isStudent=false) (readme.examples.FeatureExtractorSpec$1$Person <1234789>) ◆ ▶ its.definedIn(FeatureExtractorSpec.kt:52): "Robert" <1234789> ◾ starts with: "Pe" <1234789> ◾ ends with: "er" <1234789> ◆ ▶ its.definedIn(FeatureExtractorSpec.kt:58): "Stoll" <1234789> ◾ equals: "Dummy" <1234789>
One drawback of its (which we plan to improve but most likely not before we drop support for Kotlin < 1.5) is that reading the resulting feature description does not immediately tell us what feature we extracted.
That is where the feature function comes into play. It is based on reflection and uses the name of the feature as description. Following the first example rewritten to feature.
expect(myPerson)
.feature({ f(it::isStudent) }) { toEqual(true) } // fails, subject still Person afterwards
.feature { f(it::fullName) } // not evaluated anymore, subject String afterwards
.toStartWith("rob") // not evaluated anymore
expected that subject: Person(firstName=Robert, lastName=Stoll, isStudent=false) (readme.examples.FeatureExtractorSpec$1$Person <1234789>)
◆ ▶ isStudent: false
◾ equals: true
The report reads much nicer now:
I expected that the subject of the assertion, which is actually the Person(...), respectively its property
isStudent, which is actuallyfalse, equalstrue
The drawback of feature compared to its is its syntax. Certainly, one has to get used to it first. Another is that you might run into Ambiguity Problems due to Kotlin bugs.
feature has several overloads, we are looking at the one expecting a lambda in which you have to provide a MetaFeature. Creating a MetaFeature is done via the function f by passing in a bounded reference of the corresponding property or method (including arguments if required). it within the MetaFeature-provider-lambda refers to the subject of the assertion (myPerson in the above example).
Also feature follows the common pattern of having two overloads where the second expects an assertionCreator-lambda. Following the second example rewritten from its to feature:
expect(myPerson) { // forms an assertion group block
feature({ f(it::firstName) }) { // forms an assertion group block
toStartWith("Pe") // fails
toEndWith("er") // is evaluated nonetheless
} // fails as a whole
// still evaluated, as it is in outer assertion group block
feature { f(it::lastName) }.toEqual("Dummy")
}
expected that subject: Person(firstName=Robert, lastName=Stoll, isStudent=false) (readme.examples.FeatureExtractorSpec$1$Person <1234789>)
◆ ▶ firstName: "Robert" <1234789>
◾ starts with: "Pe" <1234789>
◾ ends with: "er" <1234789>
◆ ▶ lastName: "Stoll" <1234789>
◾ equals: "Dummy" <1234789>
Atrium provides several shortcuts for commonly used properties so that you can use them instead of writing its { ... } / feature(...) all the time. For instance, message for Throwable (see Expect an Exception), first and second for Pair and others. Please open a feature request in case you miss a shortcut.
💬
Wrap each property into an assertion function?
You might be asking yourself whether it is better to write an own assertion function or use feature.
The only drawback of using an existing property is that a few more key strokes are required compared to writing an own assertion function once and then reuse it (as we did with message). Yet, we do not recommend to write an own assertion function for every single property. We think it makes sense to add one if you use it a lot and (preferably) it is a stable API. Why not always? Because one quickly forgets to rename the assertion function if the property as such is renamed (e.g., as part of an IDE refactoring). As you can see, you would need to keep the property name and the name of the assertion function in sync to be meaningful (otherwise one gets quickly confused or has to remember two names for the same thing).
Writing assertion functions for methods is a different story though, especially due to overload bugs in Kotlin. Also, code completion is not yet as good as it should be when it comes to methods. Last but not least, in case it is not always safe to call a method (e.g. List.get => IndexOutOfBound) then it makes sense to wrap it into an assertion function and use _logic.extractFeature instead.
Last but not least, let us have a look at an example where a method with arguments is used as feature:
expect(myPerson)
.feature { f(it::nickname, false) } // subject narrowed to String
.toEqual("Robert aka. Stoll") // fails
.toStartWith("llotS") // not evaluated anymore
expected that subject: Person(firstName=Robert, lastName=Stoll, isStudent=false) (readme.examples.FeatureExtractorSpec$1$Person <1234789>)
◆ ▶ nickname(false): "Mr. Robert" <1234789>
◾ equals: "Robert aka. Stoll" <1234789>
f supports methods with up to 5 arguments.
Atrium provides shortcuts for commonly used methods, e.g. List.get, Map.getExisting, Optional.toBePresent or Result.toBeSuccess where all of them include some additional checking (index bound, existence of the key within the map etc.) Please open a feature request in case you miss a shortcut.
💬
Write own feature assertion functions with additional checks.
Atrium provides a feature extractor which allows making feature assertions in a safe way in case the extraction is only valid for certain subjects. It is inter alia used for List.get
Arbitrary Features
A feature does not necessarily have to be directly related to the subject as properties or method calls do. Either use its the overload of feature which expects a feature description in form of a String as first argument. Following an example using feature.
data class FamilyMember(val name: String)
data class Family(val members: List<FamilyMember>)
val myFamily = Family(listOf(FamilyMember("Robert")))
expect(myFamily)
.feature("number of members", { members.size }) { toEqual(1) } // subject still Family afterwards
.feature("first member's name") { members.first().name } // subject narrowed to String
.toEqual("Peter")
expected that subject: Family(members=[FamilyMember(name=Robert)]) (readme.examples.FeatureExtractorSpec$1$Family <1234789>)
◆ ▶ first member's name: "Robert" <1234789>
◾ equals: "Peter" <1234789>
Also this version of feature provides two different kind of overloads:
-
the first expects a feature description and a feature-provider-lambda This overload narrows the subject to the feature, meaning a subsequent call in the fluent chain is about the feature and not the previous subject.
-
the second expects an
assertionCreator-lambda in addition, in which you can define sub-assertions for the feature. AnassertionCreator-lambda has always the semantic of an assertion group block or in other words, not-fail fast. It has also the benefit, that Atrium can provide those sub-assertions in error reporting, Moreover, the subject stays the same so that subsequent calls are still about the same subject.
As you can see, Atrium provides a generic way to postulate assertions about features. Yet, if you use such feature assertion often or it gets more complicated, then it might be worth to write an own assertion function where we recommend to use feature over its.
Within Assertion Functions
In case you write an own assertion function, then we discourage two things:
- using
itsbecause the reporting reads less nice and it is also less efficient thanfeature - using
featurewith aMetaFeature-provider-lambda (as shown in Property and Methods)
Instead, we encourage you to pass a class references to feature. This has the benefit, that we can always show the feature name, also in case a previous feature extraction or subject transformation failed. Following an example:
fun <F : Any, T : Pair<F, *>> Expect<T>.firstToBeDoneWrong(expected: F) =
feature({ f(it::first) }) { toEqual(expected) }
fun <F : Any, T : Pair<F, *>> Expect<T>.firstToBe(expected: F) =
feature(Pair<F, *>::first) { toEqual(expected) }
expect(listOf(1 to "a", 2 to "b")).get(10) {
firstToBeDoneWrong(1)
firstToBe(1)
}
expected that subject: [(1, a), (2, b)] (java.util.Arrays.ArrayList <1234789>)
◆ ▶ get(10): ❗❗ index out of bounds
» ▶ CANNOT show description as it is based on subject which is not defined:
◾ equals: 1 (kotlin.Int <1234789>)
» ▶ first:
◾ equals: 1 (kotlin.Int <1234789>)
Also, this version of feature provides to kind of overloads, one without and one with assertionCreator-lambda. (see for instance Arbitrary Features for more information).
Ambiguity Problems
Unfortunately there are several Kotlin bugs when it comes to overloading, especially in conjunction with KFunction (see Kotlin Bugs and upvote in case you run into one). It might happen that you run into such issues using feature in conjuction with a MetaFeature-provider-lambda (as shown in Property and Methods). However, Atrium provides alternative functions next to f within the MetaFeature-provider-lambda to disambiguate the situation. Use p for properties and f0 to f5 for methods. Likely you need to specify the type parameters manually as Kotlin is not able to infer them correctly.
class WorstCase {
val propAndFun: Int = 1
fun propAndFun(): Int = 1
fun overloaded(): Int = 1
fun overloaded(b: Boolean): Int = 1
}
expect(WorstCase()) {
feature { p<Int>(it::propAndFun) }
feature { f0<Int>(it::propAndFun) }
feature { f0<Int>(it::overloaded) }
feature { f1<Boolean, Int>(it::overloaded, true) }.toEqual(1)
}
Notice, that you might run into the situation that Intellij is happy but the compiler is not. For instance, Intellij will suggest that you can remove the type parameters in the above example. Yet, if you do so, then the compiler will fail, mentioning ambiguous overloads. Most of the time this problem stems from the reason that Intellij is using a newer Kotlin version to analyse than the one you compile your project with.
Next to using the alternative functions, you could also use its or the overload of feauture which expects a String as description (as shown in arbitrary features.
Property does not exist
In case you deal with Java code and are using feature, then you might run into the problem that a property does not exist. This is due to the fact that Kotlin only provides syntactic sugar to access a getter via property syntax. In such a case, use the get... method instead. For instance:
// java
class A {
public String getFoo() { return "bar"; }
}
// kotlin
val a = A()
a.foo // syntactic sugar, accesses getFoo via property
expect(a)
// feature{ f(it::foo) } // would result in a compile error
.feature { f(it::getFoo) } // works
.startsWith(...)
Type Assertions
interface SuperType
data class SubType1(val number: Int) : SuperType
data class SubType2(val word: String, val flag: Boolean) : SuperType
val x: SuperType = SubType2("hello", flag = true)
expect(x).toBeAnInstanceOf<SubType1>()
.feature { f(it::number) }
.toEqual(2)
expected that subject: SubType2(word=hello, flag=true) (readme.examples.SubType2 <1234789>)
◆ is instance of type: SubType1 (readme.examples.SubType1)
You can narrow a type with the toBeA function. On one hand it checks that the subject of the current assertion (x in the above example) is actually the expected type and on the other hand it turns the subject into this type. This way you can make specific assertions which are only possible for the corresponding type -- for instance, considering the above example, number is not available on SuperType but only on SubType1.
expect(x).toBeAnInstanceOf<SubType2> {
feature { f(it::word) }.toEqual("goodbye")
feature { f(it::flag) }.toEqual(false)
}
expected that subject: SubType2(word=hello, flag=true) (readme.examples.SubType2 <1234789>)
◆ ▶ word: "hello" <1234789>
◾ equals: "goodbye" <1234789>
◆ ▶ flag: true
◾ equals: false
There are two toBeA overloads:
- the first (shown in the first example) is parameterless and turns only the subject into the expected type; failing to do so cannot include additional information in error reporting though.
- the second (shown in the second example) expects an
assertionCreator-lambda in which you can define sub-assertions. AnassertionCreator-lambda has always the semantic of an assertion group block -- as a recapitulation, assertions in an assertion group block are all evaluated and failures are reported at the end of the block. It has also the benefit, that Atrium can provide those sub-assertions in error reporting, showing some additional context in case of a failure.
Nullable Types
Let us look at the case where the subject of the assertion has a nullable type.
val slogan1: String? = "postulating assertions made easy"
expect(slogan1).toEqual(null)
expected that subject: "postulating assertions made easy" <1234789>
◆ equals: null
val slogan2: String? = null
expect(slogan2).toEqual("postulating assertions made easy")
expected that subject: null
◆ equals: "postulating assertions made easy" <1234789>
On one hand, you can use toEqual and pass the same type -- String? in the above example, so in other words either null as in the first example or a String as in the second example. On the other hand, you can use notToEqualNull to turn the subject into its non-null version. This is a shortcut for toBeA<Xy> where Xy is the non-nullable type (see Type Assertions). Following an example:
expect(slogan2) // subject has type String?
.notToEqualNull() // subject is narrowed to String
.toStartWith("atrium")
expected that subject: null
◆ is instance of type: String (kotlin.String) -- Class: java.lang.String
Since notToEqualNull delegates to toBeA it also provides two overloads, one without (example above) and one with assertionCreator-lambda (example below); see Type Assertions for more information on the difference of the overloads.
expect(slogan2).notToEqualNull { toStartWith("atrium") }
expected that subject: null
◆ is instance of type: String (kotlin.String) -- Class: java.lang.String
» starts with: "atrium" <1234789>
Atrium provides one additional function which is intended for data driven testing involving nullable types and is explained in the corresponding section.
👓
dealing a lot with nullable types from Java...
... in this case we recommend having a look at the Java Interoperability section.
Collection Assertions
Atrium provides assertion builders which allow to make sophisticated toContain assertions for Iterable<T>. Such a building process allows you to define very specific assertions, where the process is guided by a fluent builder pattern. You can either use such an Assertion Builder to create a specific assertion or use one of the Shortcut Functions in case you have kind of a common case. The following sub sections show both use cases by examples.
Shortcut Functions
expect(listOf(1, 2, 2, 4)).toContain(2, 3)
expected that subject: [1, 2, 2, 4] (java.util.Arrays.ArrayList <1234789>)
◆ contains, in any order:
⚬ an element which equals: 3 (kotlin.Int <1234789>)
» but no such element was found
The assertion function toContain(2, 3) is a shortcut for using a Sophisticated Assertion Builder -- it actually calls toContain.inAnyOrder.atLeast(1).values(2, 3). This is reflected in the output, which tells us that we expected that the number of such entries, which is actually 0, is at least: 1.
👓
and what about expected value 2?
Exactly, what about the expected value 2, why do we not see anything about it in the output? The output does not show anything about the expected value 2 because the default reporter reports only failing assertions.
Back to the shortcut functions.
Next to expecting that certain values are contained in or rather returned by an Iterable, Atrium allows us to use an assertionCreator-lambda to identify an element (an assertionCreator-lambda can also be thought of as matcher / predicate in this context). An element is considered as identified, if it holds all specified assertions. Following an example:
expect(listOf(1, 2, 2, 4)).toContain(
{ toBeLessThan(0) },
{ toBeGreaterThan(2).toBeLessThan(4) }
)
expected that subject: [1, 2, 2, 4] (java.util.Arrays.ArrayList <1234789>)
◆ contains, in any order:
⚬ an element which:
» is less than: 0 (kotlin.Int <1234789>)
» but no such element was found
⚬ an element which:
» is greater than: 2 (kotlin.Int <1234789>)
» is less than: 4 (kotlin.Int <1234789>)
» but no such element was found
In the above example, neither of the two lambdas matched any elements and thus both are reported as failing (sub) assertions.
Another toContain shortcut function which Atrium provides for Iterable<T> is kind of the opposite of inAnyOrder.atLeast(1) and is named toContainExactly. Again, Atrium provides two overloads for it, one for values, e.g. toContainExactly(1, 2) which calls toContain.inOrder.only.values(1, 2) and a second one which expects one or more assertionCreator-lambda, e.g. toContainExactly( { toBeGreaterThan(5) }, { toBeLessThan(10) }) which calls toContain.inOrder.only.elements({ toBeGreaterThan(5) }, { toBeLessThan(10) }). We will spare the examples here and show them in the following sections. Notice that you can pass null to toContainExactly instead of an assertionCreator-lambda to match null. This makes of course only sense if your Iterable contains nullable elements.
Atrium provides also a notToContain shortcut function. Furthermore, it provides aliases for toContain and notToContain named toHaveNextAndAny and toHaveNextAndNone,
which might be a better choice if you think in terms of: expect a predicate holds. These two are completed with an toHaveNextAndAll assertion function.
Following each in action:
expect(listOf(1, 2, 3, 4)).toHaveElementsAndAny {
toBeLessThan(0)
}
expected that subject: [1, 2, 3, 4] (java.util.Arrays.ArrayList <1234789>)
◆ contains, in any order:
⚬ an element which:
» is less than: 0 (kotlin.Int <1234789>)
» but no such element was found
expect(listOf(1, 2, 3, 4)).toHaveElementsAndNone {
toBeGreaterThan(2)
}
expected that subject: [1, 2, 3, 4] (java.util.Arrays.ArrayList <1234789>)
◆ does not contain:
⚬ an element which:
» is greater than: 2 (kotlin.Int <1234789>)
❗❗ following elements were mismatched:
⚬ index 2: 3 (kotlin.Int <1234789>)
⚬ index 3: 4 (kotlin.Int <1234789>)
expect(listOf(1, 2, 3, 4)).toHaveElementsAndAll {
toBeGreaterThan(2)
}
expected that subject: [1, 2, 3, 4] (java.util.Arrays.ArrayList <1234789>)
◆ all entries:
» is greater than: 2 (kotlin.Int <1234789>)
❗❗ following elements were mismatched:
⚬ index 0: 1 (kotlin.Int <1234789>)
⚬ index 1: 2 (kotlin.Int <1234789>)
Sophisticated Assertion Builders
Sophisticated assertion builders implement a fluent builder pattern. To use the assertion builder for sophisticated Iterable<T>-toContain-assertions, you can type toContain -- as you would when using the Shortcut Functions toContain -- but type . as next step (so that you are using the property toContain instead of one of the shortcut functions). Currently, the builder provides two options, either inAnyOrder or inOrder. In case you are using an IDE, you do not really have to think too much -- use code completion; the fluent builders will guide you through your decision-making
Following on the last section we will start with an inOrder example:
expect(listOf(1, 2, 2, 4)).toContain.inOrder.only.entries({ toBeLessThan(3) }, { toBeLessThan(2) })
expected that subject: [1, 2, 2, 4] (java.util.Arrays.ArrayList <1234789>)
◆ ▶ size: 4 (kotlin.Int <1234789>)
◾ equals: 2 (kotlin.Int <1234789>)
◆ contains only, in order:
✔ ▶ element 0: 1 (kotlin.Int <1234789>)
◾ is less than: 3 (kotlin.Int <1234789>)
✘ ▶ element 1: 2 (kotlin.Int <1234789>)
◾ is less than: 2 (kotlin.Int <1234789>)
❗❗ additional elements detected:
⚬ element 2: 2 (kotlin.Int <1234789>)
⚬ element 3: 4 (kotlin.Int <1234789>)
Since we have chosen the only option, Atrium shows us a summary where we see three things:
- Whether a specified
assertionCreator-lambda matched (signified by✔or✘) the corresponding element or not (e.g.✘ ▶ entry 1:was2and we expected, itis less than 2) - Whether the expected size was correct or not (
✘ ▶ size:was4, we expected it,to be: 2-- see also Property Assertions) - and last but not least, mismatches or additional elements as further clue (
❗❗ additional elements detected).
💬
too verbose?
As side notice, in case you are dealing with large Iterable and do not want such a verbose output, then let use know by up-voting https://github.com/robstoll/atrium/issues/292 So far the verbose output was always handy for us, but you might have other test cases than we have. Also notice, that Atrium will not deal with infinite Iterables, i.e. you need to use take(100) or the like first.
Following one more example for inOrder as well as a few examples for inAnyOrder. We think explanations are no longer required at this stage. In case you have a question (no matter about which section), then please turn up in the atrium Slack channel (Invite yourself in case you do not have an account yet) and we happily answer your question there.
expect(listOf(1, 2, 2, 4)).toContain.inOrder.only.values(1, 2, 2, 3, 4)
expected that subject: [1, 2, 2, 4] (java.util.Arrays.ArrayList <1234789>)
◆ ▶ size: 4 (kotlin.Int <1234789>)
◾ equals: 5 (kotlin.Int <1234789>)
◆ contains only, in order:
✔ ▶ element 0: 1 (kotlin.Int <1234789>)
◾ equals: 1 (kotlin.Int <1234789>)
✔ ▶ element 1: 2 (kotlin.Int <1234789>)
◾ equals: 2 (kotlin.Int <1234789>)
✔ ▶ element 2: 2 (kotlin.Int <1234789>)
◾ equals: 2 (kotlin.Int <1234789>)
✘ ▶ element 3: 4 (kotlin.Int <1234789>)
◾ equals: 3 (kotlin.Int <1234789>)
✘ ▶ element 4: ❗❗ hasNext() returned false
» equals: 4 (kotlin.Int <1234789>)
expect(listOf(1, 2, 2, 4)).toContain.inAnyOrder.atLeast(1).butAtMost(2).entries({ toBeLessThan(3) })
expected that subject: [1, 2, 2, 4] (java.util.Arrays.ArrayList <1234789>)
◆ contains, in any order:
⚬ an element which:
» is less than: 3 (kotlin.Int <1234789>)
⚬ ▶ number of such entries: 3
◾ is at most: 2
expect(listOf(1, 2, 2, 4)).toContain.inAnyOrder.only.values(1, 2, 3, 4)
expected that subject: [1, 2, 2, 4] (java.util.Arrays.ArrayList <1234789>)
◆ contains only, in any order:
✔ an element which equals: 1 (kotlin.Int <1234789>)
✔ an element which equals: 2 (kotlin.Int <1234789>)
✘ an element which equals: 3 (kotlin.Int <1234789>)
✔ an element which equals: 4 (kotlin.Int <1234789>)
❗❗ following elements were mismatched:
⚬ 2 (kotlin.Int <1234789>)
expect(listOf(1, 2, 2, 4)).toContain.inAnyOrder.only.values(4, 3, 2, 2, 1)
expected that subject: [1, 2, 2, 4] (java.util.Arrays.ArrayList <1234789>)
◆ ▶ size: 4 (kotlin.Int <1234789>)
◾ equals: 5 (kotlin.Int <1234789>)
◆ contains only, in any order:
✔ an element which equals: 4 (kotlin.Int <1234789>)
✘ an element which equals: 3 (kotlin.Int <1234789>)
✔ an element which equals: 2 (kotlin.Int <1234789>)
✔ an element which equals: 2 (kotlin.Int <1234789>)
✔ an element which equals: 1 (kotlin.Int <1234789>)
Map Assertions
Map assertions are kind of very similar to Collection Assertions, also regarding reporting. That is the reason why we are not going into too much detail here because we assume you are already familiar with it.
We provide again Shortcut Functions for the most common scenarios and more Sophisticated Assertion Builder for the other cases.
Shortcut Functions
expect(mapOf("a" to 1, "b" to 2)).toContain("c" to 2, "a" to 1, "b" to 1)
expected that subject: {a=1, b=2} (java.util.LinkedHashMap <1234789>)
◆ contains, in any order:
⚬ ▶ entry "c": ❗❗ key does not exist
» equals: 2 (kotlin.Int <1234789>)
⚬ ▶ entry "b": 2 (kotlin.Int <1234789>)
◾ equals: 1 (kotlin.Int <1234789>)
Next to making assertions based on key-value Pairs one can also define sub assertions for the value of an entry with the help of the parameter object KeyValue:
expect(mapOf("a" to 1, "b" to 2)).toContain(
KeyValue("c") { toEqual(2) },
KeyValue("a") { toBeGreaterThan(2) },
KeyValue("b") { toBeLessThan(2) }
)
expected that subject: {a=1, b=2} (java.util.LinkedHashMap <1234789>)
◆ contains, in any order:
⚬ ▶ entry "c": ❗❗ key does not exist
» equals: 2 (kotlin.Int <1234789>)
⚬ ▶ entry "a": 1 (kotlin.Int <1234789>)
◾ is greater than: 2 (kotlin.Int <1234789>)
⚬ ▶ entry "b": 2 (kotlin.Int <1234789>)
◾ is less than: 2 (kotlin.Int <1234789>)
In case you expect that a map only contains certain entries, then you can use the shortcut toContainOnly. Again both overloads are provided, one for key-value Pairs:
expect(mapOf("a" to 1, "b" to 2)).toContainOnly("b" to 2)
expected that subject: {a=1, b=2} (java.util.LinkedHashMap <1234789>)
◆ ▶ size: 2 (kotlin.Int <1234789>)
◾ equals: 1 (kotlin.Int <1234789>)
◆ contains only, in any order:
✔ ▶ entry "b": 2 (kotlin.Int <1234789>)
◾ equals: 2 (kotlin.Int <1234789>)
❗❗ additional entries detected:
⚬ entry "a": 1 (kotlin.Int <1234789>)
And the other overload which expects a KeyValue and allows defining sub asertions for the value:
expect(mapOf("a" to 1, "b" to 2)).toContainOnly(
KeyValue("c") { toEqual(2) },
KeyValue("a") { toBeLessThan(2) },
KeyValue("b") { toBeLessThan(2) }
)
expected that subject: {a=1, b=2} (java.util.LinkedHashMap <1234789>)
◆ ▶ size: 2 (kotlin.Int <1234789>)
◾ equals: 3 (kotlin.Int <1234789>)
◆ contains only, in any order:
✘ ▶ entry "c": ❗❗ key does not exist
» equals: 2 (kotlin.Int <1234789>)
✔ ▶ entry "a": 1 (kotlin.Int <1234789>)
◾ is less than: 2 (kotlin.Int <1234789>)
✘ ▶ entry "b": 2 (kotlin.Int <1234789>)
◾ is less than: 2 (kotlin.Int <1234789>)
Sophisticated Assertion Builders
Most functionality for Map.toContain are provided as shortcut functions but there is a handy one in case you deal with ordered Maps: .toContain.inOrder.only
There are multiple methods finalising the building process : entry/entries/entriesOf where entry and entries again provide two overloads, one expecting key-value Pairs:
expect(mapOf("a" to 1, "b" to 2)).toContain.inOrder.only.entries("b" to 2, "a" to 1)
expected that subject: {a=1, b=2} (java.util.LinkedHashMap <1234789>)
◆ contains only, in order:
✘ ▶ element 0: a=1 (java.util.LinkedHashMap.Entry <1234789>)
◾ ▶ key: "a" <1234789>
◾ equals: "b" <1234789>
◾ ▶ value: 1 (kotlin.Int <1234789>)
◾ equals: 2 (kotlin.Int <1234789>)
✘ ▶ element 1: b=2 (java.util.LinkedHashMap.Entry <1234789>)
◾ ▶ key: "b" <1234789>
◾ equals: "a" <1234789>
◾ ▶ value: 2 (kotlin.Int <1234789>)
◾ equals: 1 (kotlin.Int <1234789>)
And the other expecting KeyValues which allow specifying sub assertions for the value
expect(mapOf("a" to 1, "b" to 2)).toContain.inOrder.only.entries(
KeyValue("a") { toBeLessThan(2) },
KeyValue("b") { toBeLessThan(2) })
expected that subject: {a=1, b=2} (java.util.LinkedHashMap <1234789>)
◆ contains only, in order:
✔ ▶ element 0: a=1 (java.util.LinkedHashMap.Entry <1234789>)
◾ ▶ key: "a" <1234789>
◾ equals: "a" <1234789>
◾ ▶ value: 1 (kotlin.Int <1234789>)
◾ is less than: 2 (kotlin.Int <1234789>)
✘ ▶ element 1: b=2 (java.util.LinkedHashMap.Entry <1234789>)
◾ ▶ key: "b" <1234789>
◾ equals: "b" <1234789>
◾ ▶ value: 2 (kotlin.Int <1234789>)
◾ is less than: 2 (kotlin.Int <1234789>)
Others
In case you want to postulate an assertion about a value of one particular key, then you can use getExisting. For instance:
data class Person(val firstName: String, val lastName: String, val age: Int)
val bernstein = Person("Leonard", "Bernstein", 50)
expect(mapOf("bernstein" to bernstein))
.getExisting("bernstein") {
feature { f(it::firstName) }.toEqual("Leonard")
feature { f(it::age) }.toEqual(60)
}
.getExisting("einstein") {
feature { f(it::firstName) }.toEqual("Albert")
}
expected that subject: {bernstein=Person(firstName=Leonard, lastName=Bernstein, age=50)} (java.util.Collections.SingletonMap <1234789>)
◆ ▶ get("bernstein"): Person(firstName=Leonard, lastName=Bernstein, age=50) (readme.examples.MostExamplesSpec$1$Person <1234789>)
◾ ▶ age: 50 (kotlin.Int <1234789>)
◾ equals: 60 (kotlin.Int <1234789>)
In case you want to make an assertion only about the keys or values of the Map then you can use keys or values:
expect(mapOf("a" to 1, "b" to 2)) {
keys { toHaveElementsAndAll { toStartWith("a") } }
values { toHaveElementsAndNone { toBeGreaterThan(1) } }
}
expected that subject: {a=1, b=2} (java.util.LinkedHashMap <1234789>)
◆ ▶ keys: [a, b] (java.util.LinkedHashMap.LinkedKeySet <1234789>)
◾ all entries:
» starts with: "a" <1234789>
❗❗ following elements were mismatched:
⚬ index 1: "b" <1234789>
◆ ▶ values: [1, 2] (java.util.LinkedHashMap.LinkedValues <1234789>)
◾ does not contain:
⚬ an element which:
» is greater than: 1 (kotlin.Int <1234789>)
❗❗ following elements were mismatched:
⚬ index 1: 2 (kotlin.Int <1234789>)
Last but not least, you can use the non-reporting asEntries() function which turns Expect<Map<K, V>> into an Expect<Set<Map.Entry<K, V>> and thus allows that you can use all the assertion functions and sophisticated builders shown in Collection Assertions.
There should seldom be a need for it but in case you want to make also sub assertions for the key, then it will come in handy:
expect(linkedMapOf("a" to 1, "b" to 2)).asEntries().toContain.inOrder.only.entries(
{ toEqualKeyValue("a", 1) },
{
key.toStartWith("a")
value.toBeGreaterThan(2)
}
)
expected that subject: {a=1, b=2} (java.util.LinkedHashMap <1234789>)
◆ contains only, in order:
✔ ▶ element 0: a=1 (java.util.LinkedHashMap.Entry <1234789>)
◾ ▶ key: "a" <1234789>
◾ equals: "a" <1234789>
◾ ▶ value: 1 (kotlin.Int <1234789>)
◾ equals: 1 (kotlin.Int <1234789>)
✘ ▶ element 1: b=2 (java.util.LinkedHashMap.Entry <1234789>)
◾ ▶ key: "b" <1234789>
◾ starts with: "a" <1234789>
◾ ▶ value: 2 (kotlin.Int <1234789>)
◾ is greater than: 2 (kotlin.Int <1234789>)
toEqualKeyValue as well as key and value are assertion functions defined for Map.Entry<K, V>.
There are more assertion functions, a full list can be found in KDoc of atrium-api-fluent-en_GB.
Path Assertions
Atrium’s assertions for paths give detailed failure hints explaining what happened on the file system. For example, exists will explain which entry was the first one missing:
expect(Paths.get("/usr/bin/noprogram")).toExist()
expected that subject: /usr/bin/noprogram (sun.nio.fs.UnixPath <1234789>)
◆ to: exist
» the closest existing parent directory is /usr/bin
Atrium will give details about why something cannot be accessed, for example when checking whether a file is writable:
expect(Paths.get("/root/.ssh/config")).toBeWritable()
expected that subject: /root/.ssh/config (sun.nio.fs.UnixPath <1234789>)
◆ is: writable
» failure at parent path: /root (sun.nio.fs.UnixPath <1234789>)
» access was denied
» the owner is root, the group is root
» the permissions are u=rwx g= o=
Even in more complicated scenarios, Atrium explains step by step what happened:
val directory = Files.createDirectory(tmpdir.resolve("atrium-path"))
val file = Files.createFile(directory.resolve("file"))
val filePointer = Files.createSymbolicLink(directory.resolve("directory"), file)
expect(filePointer.resolve("subfolder/file")).toBeARegularFile()
expected that subject: /tmp/atrium-path/directory/subfolder/file (sun.nio.fs.UnixPath <1234789>)
◆ is: a file
» followed the symbolic link /tmp/atrium-path/directory to /tmp/atrium-path/file
» failure at parent path: /tmp/atrium-path/file (sun.nio.fs.UnixPath <1234789>)
» was a file instead of a directory
Attaching a Reason
In case you want to add further information to an assertion, e.g. state the reason why you expect it to hold, you can use because:
expect("filename?")
.because("? is not allowed in file names on Windows") {
notToContain("?")
}
expected that subject: "filename?" <1234789>
◆ does not contain:
⚬ value: "?" <1234789>
⚬ ▶ number of matches: 1
◾ is: 0 (kotlin.Int <1234789>)
ℹ because: ? is not allowed in file names on Windows
💬
Use because only to give reasons for non-obvious assertions
because can be a useful tool for explaining why there is a certain assertion. Sometimes it is not directly obvious why one should expect something. In such cases, using because can make your code, and your error messages, easier to understand for other developers (including yourself in three months).
Having said that, you should not use because if you are missing a specific predefined assertion function. You can use a feature assertion, write your own expectation function or propose an addition to Atrium in such cases.
Just like code comments, because can be valuable, but should not be overused.
Data Driven Testing
Atrium is not intended for data driven testing in the narrowed sense in terms that it cannot produce multiple tests. This is the responsibility of your test runner. However, Atrium let you define multiple assertions within one test and reports them all if you want. In this sense it can be used for data driven testing. This is especially helpful in case your test runner does not support data driven testing (or other mechanisms like hierarchical or dynamic tests). As an example, Atrium can help you writing data driven tests in a common module of a multiplatform-project.
The trick is to wrap your assertions into an assertion group block and create Feature Assertions. Following an example:
fun myFun(i: Int) = (i + 97).toChar()
expect("calling myFun with...") {
mapOf(
1 to 'a',
2 to 'c',
3 to 'e'
).forEach { (arg, result) ->
feature { f(::myFun, arg) }.toEqual(result)
}
}
expected that subject: "calling myFun with..." <1234789>
◆ ▶ myFun(1): 'b'
◾ equals: 'a'
◆ ▶ myFun(3): 'd'
◾ equals: 'e'
Depending on the chosen reporting style it will only show the failing cases (default behaviour). This is also the reason why the call of myFun(2) is not listed (as the result is c as expected).
Please create a feature request if you want to see a summary, meaning also successful assertions -- we happily add more functionality if it is of use for someone.
Following another example which involves an assertion creator lambda and not only a simple toEqual check. We are going to reuse the myFun from above:
import ch.tutteli.atrium.logic.utils.expectLambda
expect("calling myFun with ...") {
mapOf(
1 to expectLambda<Char> { toBeLessThan('f') },
2 to expectLambda { toEqual('c') },
3 to expectLambda { toBeGreaterThan('e') }
).forEach { (arg, assertionCreator) ->
feature({ f(::myFun, arg) }, assertionCreator)
}
}
expected that subject: "calling myFun with ..." <1234789>
◆ ▶ myFun(3): 'd'
◾ is greater than: 'e'
The example should be self-explanatory. One detail to note though is the usage of expectLambda. It is a helper function which circumvents certain Kotlin type inference bugs (upvote them please). Writing the same as mapOf<Int, Expect<Char>.() -> Unit>( 1 to { ... } ) would not work as the type for a lambda involved in a Pair is not (yet) inferred correctly by Kotlin.
There is one last function worth mentioning here which comes in handy in data-driven testing in case the subject has a nullable type
If you wish to make sub-assertions on the non-nullable type of the subject, then you can use toEqualNullIfNullGivenElse which accepts an assertionCreator-lambda or null. It is short for if (assertionCreatorOrNull == null) toEqual(null) else notToEqual(assertionCreatorOrNull). Following another fictional example which illustrates toEqualNullIfNullGivenElse (we are reusing myFun from above):
fun myNullableFun(i: Int) = if (i > 0) i.toString() else null
expect("calling myNullableFun with ...") {
mapOf(
Int.MIN_VALUE to expectLambda<String> { toContain("min") },
-1 to null,
0 to null,
1 to expectLambda { toEqual("1") },
2 to expectLambda { toEndWith("2") },
Int.MAX_VALUE to expectLambda { toEqual("max") }
).forEach { (arg, assertionCreatorOrNull) ->
feature { f(::myNullableFun, arg) }.toEqualNullIfNullGivenElse(assertionCreatorOrNull)
}
}
expected that subject: "calling myNullableFun with ..." <1234789>
◆ ▶ myNullableFun(-2147483648): null
» contains:
⚬ value: "min" <1234789>
» but no match was found
◆ ▶ myNullableFun(2147483647): "2147483647" <1234789>
◾ equals: "max" <1234789>
Further Examples
Atrium supports further assertion builders (e.g, for CharSequence) as well as assertion functions which have not been shown in the examples. Have a look at apis/differences.md for a few more examples. This site contains also a list of all APIs with links to their assertion function catalogs.
You can also have a look at the specifications for more examples.
Sample Projects
Have a look into the samples folder, it currently contains sample projects for
Are you using a different runner? A PR would be appreciated
Third-party Extensions
Following extensions are maintained outside of this repository.
- atrium-gradle-testkit: Atrium assertions to test Gradle plugins with TestKit.
How is Atrium different from other Assertion Libraries
The following subsections shall give you a quick overview how Atrium differ from other assertion libraries.
Ready to Help
Atrium is designed to help you whenever possible. We think this is the biggest difference to other assertion libraries and a very handy one indeed.
1. Fluent API with Code Documentation
Atrium provides a fluent API where the design focus was put on the interoperability (of the API) with the code completion functionality of your IDE. Or in other words, you can always use code completion to get direct help from your IDE. This experience is improved by providing up-to-date code documentation (in form of KDoc) for all assertion functions, so that you get the extra help needed.
💩
There is no KDoc for toEqual
There is, but IntelliJ will not show it to you due to this bug (please upvote it). You should be able to see the KDoc of other functions without problems. But in case, you can also browse the online documentation, e.g. KDoc of toEqual.
2. Additional Information in Failure Reporting
Atrium adds extra information to error messages so that you get quickly a better idea of what went wrong. For instance, for the following assertion (which fails):
expect(listOf(1, 2, 3)).toContain.inOrder.only.values(1, 3)
Atrium points out which values were found, makes an implicit assertion about the size and also states which entries were additionally contained in the list:
expected that subject: [1, 2, 3] (java.util.Arrays.ArrayList <1234789>)
◆ ▶ size: 3 (kotlin.Int <1234789>)
◾ equals: 2 (kotlin.Int <1234789>)
◆ contains only, in order:
✔ ▶ element 0: 1 (kotlin.Int <1234789>)
◾ equals: 1 (kotlin.Int <1234789>)
✘ ▶ element 1: 2 (kotlin.Int <1234789>)
◾ equals: 3 (kotlin.Int <1234789>)
❗❗ additional elements detected:
⚬ element 2: 3 (kotlin.Int <1234789>)
Let us have a look at another example.
expect(9.99f).toEqualWithErrorTolerance(10.0f, 0.01f)
The above assertion looks good at first sight but actually fails (at least on my machine). And without some extra information in the output we would believe that there is actually a bug in the assertion library itself. But Atrium shows where it goes wrong and even gives a possible hint:
expected that subject: 9.99 (kotlin.Float <1234789>)
◆ to equal (error ± 0.01): 10.0 (kotlin.Float <1234789>)
» failure might be due to using kotlin.Float, see exact check on the next line
» exact check is |9.989999771118164 - 10.0| = 0.010000228881835938 ≤ 0.009999999776482582
One last example. This time about making an assertion that a certain Throwable is thrown but the assertion fails because it was the wrong one. Atrium comes with a very useful hint, it shows the actual exception:
expect {
try {
throw UnsupportedOperationException("not supported")
} catch (t: Throwable) {
throw IllegalArgumentException("no no no...", t)
}
}.toThrow<IllegalStateException> { messageToContain("no no no") }
expected that subject: () -> kotlin.Nothing (readme.examples.MostExamplesSpec$1$39$1 <1234789>)
◆ ▶ thrown exception when called: java.lang.IllegalArgumentException
◾ is instance of type: IllegalStateException (java.lang.IllegalStateException)
» ▶ message:
◾ is instance of type: String (kotlin.String) -- Class: java.lang.String
◾ contains:
⚬ value: "no no no" <1234789>
» but no match was found
ℹ Properties of the unexpected IllegalArgumentException
» message: "no no no..." <1234789>
» stacktrace:
⚬ readme.examples.MostExamplesSpec$1$39$1.invoke(MostExamplesSpec.kt:248)
⚬ readme.examples.MostExamplesSpec$1$39$1.invoke(MostExamplesSpec.kt:22)
⚬ readme.examples.MostExamplesSpec$1$39.invoke(MostExamplesSpec.kt:272)
⚬ readme.examples.MostExamplesSpec$1$39.invoke(MostExamplesSpec.kt:22)
» cause: java.lang.UnsupportedOperationException
» message: "not supported" <1234789>
» stacktrace:
⚬ readme.examples.MostExamplesSpec$1$39$1.invoke(MostExamplesSpec.kt:246)
3. Prevents you from Pitfalls
But not enough. There are certain pitfalls when it comes to using an assertion library and Atrium tries to prevent you from those.
For instance, an overload of toEqual and of notToEqual for BigDecimal was introduced which are both deprecated and throw a PleaseReplaceException. The reason behind it? It is very likely that a user actually wants to compare that a certain BigDecimal is numerically (not) equal to another BigDecimal rather than including BigDecimal.scale in the comparison. Accordingly, the deprecation message of toEqual (notToEqual alike) explains the problem and suggests to either use toEqualNumerically or toEqualIncludingScale. And if the user should decide to use toEqualIncludingScale and at some point an assertion fails only due to the comparison of BigDecimal.scale then Atrium reminds us of the possible pitfall. For instance:
expect(BigDecimal.TEN).toEqualIncludingScale(BigDecimal("10.0"))
expected that subject: 10 (java.math.BigDecimal <1234789>)
◆ is equal (including scale): 10.0 (java.math.BigDecimal <1234789>)
ℹ notice, if you used toEqualNumerically then the assertion would have hold.
Another example are empty assertionCreator-lambdas. Getting distracted by a working colleague and taking up the work at the wrong position might sound familiar to you. For instance:
expect(listOf(1)).get(0) {}
expected that subject: [1] (java.util.Collections.SingletonList <1234789>)
◆ ▶ get(0): 1 (kotlin.Int <1234789>)
◾ at least one assertion defined: false
» You forgot to define assertions in the assertionCreator-lambda
» Sometimes you can use an alternative to `{ }` For instance, instead of `toThrow<..> { }` you should use `toThrow<..>()`
Flexibility
Another design goal of Atrium was to give you the flexibility needed but still adhere to a concise design. First and most importantly, Atrium does not enforce a certain style on your code base. Quite the contrary, it gives you the flexibility to choose a desired name for the expectation verb, it continues by providing the possibility to configure the reporting style, goes on that you can choose from different API Styles and ends that you can replace almost all components by other implementations and hook into existing.
So for instance, if you like to use an infix API, then use the bundle atrium-infix-en_GB. You prefer pure fluent and do not even want to see infix style in your code, then use atrium-fluent-en_GB which provides a pure fluent style API.
You are free to choose what fits best without introducing ambiguity etc. You could even mix up different API-styles if needed (but not without losing conciseness -- but hey, it is your decision
Migration of Deprecated Functionality
Atrium follows Semantic Versioning and tries to be binary backward compatible within a major version (since 0.6.0). Until 1.0.0 this is only true for the API level, we reserve the right to break things on the logic and core level until then. Moreover, we follow the principle that a user of Atrium has enough time to migrate its code to new functionality before a next major version. We provide this in form of @Deprecated annotations with a corresponding ReplaceWith as well as migration guides in the Release Notes. This way we hope that we provide a pleasant way to stay up-to-date without the need to migrate everything from one day to the other.
Internationalization
The last difference is not yet fully-blown implemented, but the design of Atrium has everything needed to go down the planed Roadmap. Might well be that this topic is not really a concern of yours; unless...
- you are using domain-driven-design and would like to adopt the ubiquitous language also to your test code.
- you want to document the results of your defined assertions (in different languages)
Atrium already supports APIs in two languages, and it is an easy task to translate an API to another language (hello DDD-people
Together with the HTML-Report feature (currently missing but will follow) you will be able to generate reports in different languages. Already the HTML-Report feature as such might be of your interest. You can use it to document your user stories etc (almost) for free. In case you have clients who speak different languages then the HTML-Report together with the i18n feature will be especially helpful. We should not go on here, the HTML-Report feature is not yet implemented, but you can see what kind of road we plan to go down to.
Write own Assertion Functions
Are you missing an assertion function for a specific type and the generic Feature Assertions are not good enough?
The following subsections will show how you can write your own assertion functions. A pull request of your new assertion function is very much appreciated.
Boolean based Assertions
This is kind of the simplest way of defining assertion functions. Following an example:
import ch.tutteli.atrium.logic._logic
fun Expect<Int>.toBeAMultipleOf(base: Int) =
_logic.createAndAppend("is multiple of", base) { it % base == 0 }
and its usage:
expect(12).toBeAMultipleOf(5)
expected that subject: 12 (kotlin.Int <1234789>)
◆ is multiple of: 5 (kotlin.Int <1234789>)
Let us see how we actually defined toBeAMultipleOf.
-
Choose the extension point: in our example we want to provide the assertion function for
Ints. Hence we definetoBeAMultipleOfas extension function ofExpect<Int>. -
Use the method
createAndAddAssertion(provided byExpect) which creates and adds the assertion to itself (creating alone is not enough, it needs to be added in order that it is evaluated). The methodcreateAndAddAssertionreturns itself (the sameExpect) making it easy for you to provide a fluent API as well.The method createAndAddAssertion expects:
- a either a
Stringor a Translatable as description of your assertion. - the representation of the expected value.
- and the actual check as lambda where you typically use
itwhich refers to the subject of the assertion.
- a either a
We used a String as description in the above example because we are not bothered with internationalization at this point (have a look at Internationalization if you are).
In most cases you probably use the expected value itself as its representation -- so you pass it as second argument. And finally you specify the test as such in the lambda passed as third argument.
But not all assertion functions require a value which is somehow compared against the subject -- some make an assertion about a characteristic of the subject without comparing it against an expected value. Consider the following assertion function:
import ch.tutteli.atrium.logic._logic
fun Expect<Int>.toBeEven() =
_logic.createAndAppend("is", Text("an even number")) { it % 2 == 0 }
We are using a Text here so that "an even number" is not treated as a String in reporting. Its usage looks then as follows:
expect(13).toBeEven()
expected that subject: 13 (kotlin.Int <1234789>)
◆ is: an even number
Compose Assertion Functions
So far, we core contributors ran quickly into the situation where we wanted to compose functions or reuse existing functions but with different arguments. We will show both use cases here, starting off by composing functions.
Say you want to build a toBeBetween assertion function for java.util.Date, you could write it as follows:
fun <T : Date> Expect<T>.toBeBetween(lowerBoundInclusive: T, upperBoundExclusive: T) =
toBeGreaterThanOrEqualTo(lowerBoundInclusive).and.toBeLessThan(upperBoundExclusive)
Pretty simple, isn't it? Notice though, that this function fails fast, which means, the upper bound is not evaluated if the assertion about the lower bound already fails. You need to use an assertion group block if you want that both are evaluated:
import ch.tutteli.atrium.logic._logic
fun <T : Date> Expect<T>.toBeBetween(lowerBoundInclusive: T, upperBoundExclusive: T) =
_logic.appendAsGroup {
toBeGreaterThanOrEqualTo(lowerBoundInclusive)
toBeLessThan(upperBoundExclusive)
}
Still simple enough.
💬
Why is a type parameter used in the above examples?
That is right, we used a type parameter T: Date and not Expect<Date> directly. You should always do this unless your type is final (not open) and does not have type parameters itself - but to have a simple rule, just do it. This way the assertion function is also available for sub types. This is because Expect is invariant. Following an example:
interface A { val foo get() = 1 }
class B: A
val Expect<A>.foo get() = feature(A::foo)
expect(B()).foo // does not compile as foo is only available for `Expect<A>`
So let's move on to an example which is a bit more complicated. Assume the following data class Person
data class Person(
val firstName: String,
val lastName: String,
val age: Int,
val children: Collection<Person>
// ... and others
)
Say you want to make an assertion about the number of children a person has:
fun Expect<Person>.toHaveNumberOfChildren(number: Int): Expect<Person> =
feature(Person::children) { toHaveSize(number) }
Three things to notice here:
- we make use of a feature assertion with class reference.
- We use the overload which expects an
assertionCreator-lambda. This way subsequent assertions are still made onPersonand not onchildren.
Its usage is then as follows:
expect(Person("Susanne", "Whitley", 43, listOf()))
.toHaveNumberOfChildren(2)
expected that subject: Person(firstName=Susanne, lastName=Whitley, age=43, children=[]) (readme.examples.Person <1234789>)
◆ ▶ children: [] (kotlin.collections.EmptyList <1234789>)
◾ ▶ size: 0 (kotlin.Int <1234789>)
◾ equals: 2 (kotlin.Int <1234789>)
Another example: assert the person has children which are all adults (assuming 18 is the age of majority).
fun Expect<Person>.toHaveAdultChildren(): Expect<Person> =
feature(Person::children) {
toHaveElementsAndAll {
feature(Person::age).toBeGreaterThanOrEqualTo(18)
}
}
We once again use feature with an assertion group block for the same reason as above. Note how toHaveElementsAndAll already checks that there is at least one element. I.e. it fails for a Person with 0 children, because such a person does not have adult children.
expect(Person("Susanne", "Whitley", 43, listOf()))
.toHaveAdultChildren()
expected that subject: Person(firstName=Susanne, lastName=Whitley, age=43, children=[]) (readme.examples.Person <1234789>)
◆ ▶ children: [] (kotlin.collections.EmptyList <1234789>)
◾ has: a next element
» all entries:
» ▶ age:
◾ is greater than or equal to: 18 (kotlin.Int <1234789>)
If we keep adding assertion functions involving children it might be best to provide a shortcut property and function.
val Expect<Person>.children: Expect<Collection<Person>> get() = feature(Person::children)
fun Expect<Person>.children(assertionCreator: Expect<Collection<Person>>.() -> Unit): Expect<Person> =
feature(Person::children, assertionCreator)
Notice, that we have used a class-reference and not a bounded-reference to refer to children which is best practice (see feature assertions within assertion functions). With this, we can write things like:
expect(Person("Susanne", "Whitley", 43, listOf(Person("Petra", "Whitley", 12, listOf()))))
.children { // using the fun -> assertion group, ergo sub-assertions don't fail fast
toHaveElementsAndNone {
feature { f(it::firstName) }.toStartWith("Ro")
}
toHaveElementsAndAll {
feature { f(it::lastName) }.toEqual("Whitley")
}
} // subject is still Person here
.apply { // only evaluated because the previous assertion group holds
children // using the val -> subsequent assertions are about children and fail fast
.toHaveSize(2)
.toHaveElementsAndAny {
feature { f(it::age) }.toBeGreaterThan(18)
}
} // subject is still Person here due to the `apply`
.children // using the val -> subsequent assertions are about children and fail fast
.toHaveSize(2)
expected that subject: Person(firstName=Susanne, lastName=Whitley, age=43, children=[Person(firstName=Petra, lastName=Whitley, age=12, children=[])]) (readme.examples.Person <1234789>)
◆ ▶ children: [Person(firstName=Petra, lastName=Whitley, age=12, children=[])] (java.util.Collections.SingletonList <1234789>)
◾ ▶ size: 1 (kotlin.Int <1234789>)
◾ equals: 2 (kotlin.Int <1234789>)
Enough of feature assertions. Let's move on to an example where we want to reuse an existing function but with different arguments. Say we have a function which returns a list of first name / last name Pairs. We want to assert that the pairs contain only the first name / last name pairs of certain Persons in any order. Collection Assertions will help us with this. However, toContain.inAnyOrder.values expects Pairs. So we have to map from Person to Pair upfront. As we have a variable length argument list and want to pass it to a variable length argument list, this cannot be done with a simple map from Kotlin. And it gets worse if we want to use toContain.inAnyOrder.entries which expects at least one assertionCreator-lambda (Expect<T>.() -> Unit) because Kotlin cannot infer the types automatically.
mapArguments to the rescue, you can write the assertion function as follows:
import ch.tutteli.atrium.logic.utils.mapArguments
fun <T : List<Pair<String, String>>> Expect<T>.areNamesOf(
person: Person, vararg otherPersons: Person
): Expect<T> {
val (pair, otherPairs) = mapArguments(person, otherPersons) { it.firstName to it.lastName }
return toContain.inAnyOrder.only.values(pair, *otherPairs)
}
As you can see we moved the mapping inside the function so that the consumer of our API can happily use it as follows:
expect(get...WhichReturnsPairs()).areNamesOf(fKafka, eBloch, kTucholsky)
Another fictional example, say we want to assert that the pairs have the same initials as the given persons and in the given order. Which means, this time we need to use assertionCreator-lambdas. This can be written as follows:
fun <T : List<Pair<String, String>>> Expect<T>.sameInitialsAs(
person: Person, vararg otherPersons: Person
): Expect<T> {
val (first, others) = mapArguments(person, otherPersons).toExpect<Pair<String, String>> {
first.toStartWith(it.firstName[0].toString())
second.toStartWith(it.lastName[0].toString())
}
return toContain.inOrder.only.entries(first, *others)
}
There are a few additional methods which you can call after mapArguments. See KDoc of ArgumentMapperBuilder. In case you want to provide your own implementation, it suffices to create an extension function for ArgumentMapperBuilder.
Enhanced Reporting
Composing assertion functions give already quite a bit of power to an assertion function writer. Yet, sometimes we would like to create functions which have a better error reporting than the one we get when we compose assertion functions.
_logic is the entry point to AssertionContainer which is the equivalent of Expect but on a lower level.
Following a quick overview what extension methods could be useful:
- all assertion functions on the logic level (what you have seen in Compose-assertion-functions was the API level) so that you can reuse and compose them in other ways.
changeSubjectwhich allows to change the subject either:unreported; meaning it does not show up in reporting (e.g.Expect<Array<out T>>.asList()uses it, see arrayAssertions)- reported, using
reportBuilder; meaning a subject transformation which is shown in reporting as it incorporates a transformation (e.g.toBeAuses it, see AnyAssertions)
collectwhich allows to collect assertions - especially helpful in composing assertions (see mapAssertions)extractFeaturefor feature assertions which are not always save to extract (seeList.get)
Besides, the assertionBuilder allows to create different kinds of assertions (see AssertionBuilder for more information) which can be used to create very specific assertion functions.
You can find an example in floatingPointAssertions which makes use of explanatory assertions as well as providing a failure hint.
Unfortunately we do not have the time to cover all cases, so let us know if you want to know more -- either by opening an issue or via the atrium Slack channel (Invite yourself).
Own Sophisticated Assertion Builders
Do you want to write an own sophisticated assertion builder (or extend a current with more options) instead of an assertion function? Great, we do not provide documentation yet (had only one question about it since 2017).
We are willing to provide more documentation if you need it (please open an issue). In the meantime we might help you via slack, please post your questions in the atrium Slack channel (Invite yourself in case you do not have an account yet).
Use own Expectation Verb
Atrium offers the expectation verb expect out of the box.
You can also define your own expectation verb if expect does not suite you or in case you want to change some default implementation. In order to create an own expectation verb it is sufficient to:
- Copy the file content of atriumVerbs.kt
- Create your own atriumVerbs.kt and paste the previously copied content -- notice that you can also use a
Stringfor the expectation verb in case you do not care about Internationalization - Adjust package name and
imports and renameexpectas desired (you can also leave it that way of course). - exclude
atrium-verbsfrom your dependencies. Taking the setup shown in the Installation section for the JVM platform, you would replace thedependenciesblock as follows:dependencies { testImplementation("ch.tutteli.atrium:atrium-fluent-en_GB:$atrium_version") { exclude group: 'ch.tutteli.atrium', module: 'atrium-verbs' } }
What are the benefits of creating an own expectation verb:
-
you can encapsulate the reporting style.
This is especially useful if you have multiple projects and want to have a consistent reporting style.
For instance, you could change from same-line to multi-line reporting or report not only failing but also successful assertions, change the output language etc.💬 where should I put the atriumVerbs.kt?We suggest you create an adapter project for Atrium where you specify the expectation verb. And most likely you will accumulate them with assertion functions which are so common that they appear in multiple projects -- please share them with us (get in touch with us via issue or slack) if they are not of an internal nature
😉
-
you can define some default configurations like show only failing assertions for
toContain.inOrder.only
What are the drawbacks:
- you have to maintain your expectation verb. That should not be a big deal though -- you might have to replace deprecated options by their replacement when you upgrade to a newer Atrium version but that's about it.
Use own Components
Replacing existing components with your own (or third-party) components can be done when specifying an own expectation verb via withOptions. See for instance atriumVerbs.kt which is used internally of Atrium in tests and uses a different AtriumErrorAdjuster.
Another example, say you prefer multi-line reporting over single-line reporting, then you can use withOptions as follows:
import ch.tutteli.atrium.core.ExperimentalNewExpectTypes
import ch.tutteli.atrium.creating.ExperimentalComponentFactoryContainer
import ch.tutteli.atrium.creating.build
@OptIn(ExperimentalNewExpectTypes::class, ExperimentalComponentFactoryContainer::class)
fun <T> expect(subject: T): RootExpect<T> =
RootExpectBuilder.forSubject(subject)
.withVerb("expected the subject")
.withOptions {
withComponent(TextAssertionPairFormatter::class) { c ->
TextAssertionPairFormatter.newNextLine(c.build(), c.build())
}
}
.build()
Following an example using the expectation verb
expect(10).toEqual(9)
expected the subject:
10 (kotlin.Int <1234789>)
◆ equals:
9 (kotlin.Int <1234789>)
Compare the above output with what we would get per default:
expected the subject: 10 (kotlin.Int <1234789>)
◆ to be: 9 (kotlin.Int <1234789>)
You prefer another reporting style but Atrium does not yet support it? Please let us know it by writing a feature request.
There are more options to choose from. Take a look at the DefaultComponentFactoryContainer to see the default configuration.
Internationalization
We distinguish between two use cases. You might want to generate the Report in a different language or/and you might want to use the API in a different language.
Report
Following on the example in Write own Assertion Functions we show here how you need to write the toBeAMultipleOf function, so that it supports i18n. This way the report could be generated in another language.
The difference lies in the first argument passed to createAndAddAssertion; we do no longer use a String but a proper Translatable.
import ch.tutteli.atrium.logic.*
fun Expect<Int>.toBeAMultipleOf(base: Int): Expect<Int> = _logic.run {
append(
createDescriptiveAssertion(DescriptionIntAssertion.TO_BE_A_MULTIPLE_OF, base) { it % base == 0 }
)
}
enum class DescriptionIntAssertion(override val value: String) : StringBasedTranslatable {
TO_BE_A_MULTIPLE_OF("to be a multiple of")
}
Typically, you would put DescriptionIntAssertion into an own module (jar) so that it could be replaced (with zero performance cost) by another language representation. For instance, atrium-fluent-en_GB-common uses atrium-translations-en_GB-common whereas tests of atrium-infix_en_GB-common uses atrium-translations-de_CH-common.
💬
Using a TranslationSupplier
Next to providing translations via code you can also use a TranslationSupplier based Translator by configuring the ReporterBuilder accordingly (e.g. use withDefaultTranslationSupplier instead of withoutTranslations). Atrium supports a properties files based TranslationSupplier for JVM (a supplier for JS will follow) which is more or less what ResourceBundle provides out of the box. Yet, a Translator uses a more enhanced fallback mechanism compared to a ResourceBundle. For further technical information have a look at the KDoc of Translator. Notice though, that we plan to move away from the ResourceBundle-inspired approach due to enconding problems and missing implementations on other platforms than JVM.
Notice, Atrium does not yet support the generation of multiple reports in the same test run. This might become handy if you want to generate an HTML report in different languages.
However, Atrium is designed to support this use case -- if you need this feature, then please let us know it by writing a feature request.
Let us rewrite the toBeEven assertion function from the section Write own Assertion Functions as second example:
import ch.tutteli.atrium.logic.*
fun Expect<Int>.toBeEven(): Expect<Int> = _logic.run {
append(
createDescriptiveAssertion(DescriptionBasic.IS, DescriptionIntAssertions.EVEN) { it % 2 == 0 }
)
}
enum class DescriptionIntAssertions(override val value: String) : StringBasedTranslatable {
EVEN("an even number")
}
Once again we have to wrap the text which we want to be able to exchange with another language into a Translatable. Notice also, that we are reusing a Translatable from DescriptionBasic.
API in a different Language
Following on the example in the previous section, we want to write toBeAMultipleOf in such a way that one cannot only generate a report in a different language but also that one can use the function itself in a different language. Or in other words, provide our API in a different language (the same applies if you want to provide another API style).
We split up the function in two parts: API and logic -- whereas the logic creates the assertion and the API provides a function for the user (the API as such) and merely appends the assertion created by the logic to the Expect.
Typically, you put the API function in one module (jar) and the logic in another (so that the API can be exchanged). In the logic module we define and extension method for AssertionContainer
import ch.tutteli.atrium.creating.AssertionContainer
fun AssertionContainer<Int>.toBeAMultipleOf(base: Int): Assertion =
createDescriptiveAssertion(DescriptionIntAssertion.TO_BE_A_MULTIPLE_OF, base) { it % base == 0 }
In the above example we created a simple DescriptiveAssertion with the help of createDescriptiveAssertion defined on AssertionContainer. We pass in a description (TO_BE_A_MULTIPLE_OF), use base as representation of the assertion and defined a lambda which implements a test to define whether the assertion holds or not.
In the API module we define the extension function and append the assertion to the current Expect by using logicAppend and calling the extension function from the logic module within the corresponding lambda.
import ch.tutteli.atrium.logic.*
fun Expect<Int>.toBeAMultipleOf(base: Int): Expect<Int> =
_logicAppend { toBeAMultipleOf(base) }
At first, this looks like a recursive call. But as explained, within the _logicAppend-lambda we are on the logic level and thus call the function we defined above (which just turns out to have the same name).
You are ready to go, creating an API in a different language -- e.g. in German -- is now only a routine piece of work:
import ch.tutteli.atrium.logic.*
fun Expect<Int>.istEinVielfachesVon(base: Int): Expect<Int> =
_logicAppend { toBeAMultipleOf(base) }
API Styles
Atrium supports currently two API styles: pure fluent and infix. Both have their design focus on interoperability with code completion functionality of your IDE -- so that you can let your IDE do some of the work.
Atrium is built up by different modules and it is your choice which implementation you want to use. However, this is more intended for advanced user with special requirements. Atrium provides bundle modules which bundle API, logic, core, translation as well as predefined expectation verbs, so that you just have to have a dependency on one of those bundles (kind a bit like a BOM pom in the maven world):
Have a look at apis/differences.md for more information and to see how the API styles differ.
Java Interoperability
Atrium provides some helper functions in case you have to deal with Java Code where not all types are non-nullable. Platform types are turned into a non-nullable version per default (if possible).
Yet, that might not be what you want, especially if you know that certain functions return potentially null or in other words, the return type of those functions should be treated as nullable in Kotlin. Therefore, you want to turn the platform type into the nullable version.
You need to use a cast to do this. But depending on your return type this might be cumbersome especially if you deal with type parameters. Thus, Atrium provides the following functions to ease dealing with Java Code at least for some standard cases:
nullableturns a type into a nullable type.nullableContainerturns anIterableinto an iterable with nullable element type, likewise it does the same forArray.nullableKeyMapturns aMapinto a map with a nullable key type.nullableValueMapturns aMapinto a map with a nullable value type.nullableKeyValueMapturns aMapinto a map with a nullable key and nullable value type.
KDoc - Code Documentation
The code documentation is generated with dokka and is hosted on github-pages: KDoc of atrium
Known Limitations
According to the YAGNI principle this library does not yet offer a lot of out-of-the-box assertion functions. More functions will follow but only if they are used somewhere by someone. So, let us know if you miss something by creating a feature request.
FAQ
You find frequently asked questions below. If your question is not answered below, then please do not hesitate and ask your question in the atrium Slack channel. In case you do not have an account for kotlinlang.slack.com yet, then please Invite yourself.
Are there toContain/toHaveNextAndAll/None/All expectation functions for Sequence/Array?
Atrium does not provide extension function applicable to Expect<Sequence<E>> (or Array) directly, because they would basically duplicate the functions available for Iterable<E>.
However, Atrium provides asIterable and asList so that you can turn Expect<Sequence<E>> into Expect<Iterable<E>> or Expect<List<E>>. An example:
expect(sequenceOf(1, 2, 3)).asIterable().toContain(2)
Likewise, you can turn an Expect<Array<E>>, Expect<DoubleArray> etc. into an Expect<List<E>> with asList.
Feel free vote for first class support for Array and Sequence in api-fluent.
💬
why do I not see anything about the transformation in reporting?
asIterable uses _logic.changeSubject.unreported internally which is intended for not showing up in reporting. If you would like that the transformation is reflected in reporting then you can use a regular feature assertion as follows:
expect(sequenceOf(1, 2, 3)).feature { f(it::asIterable) }.toContain(2)
Where do I find a list of all available functions?
Atrium provides KDoc for all APIs - have a look at their KDoc:
Problems in conjunction with feature
See Ambiguity Problems and Property does not exist.
Roadmap
The roadmap is maintained at atrium-roadmap. The milestones give you an overview of the planned (breaking) changes -- e.g. the changes for the next major version 1.0.0
You are invited to take part in the discussions related to design decisions, upcoming features and more. Bring in your own wishes and ideas into this process.
In case you are missing a particular assertion function in Atrium, then please open a Feature Request in this repository.
Contributors and contribute
Our thanks go to code contributors as well as other contributors (see acknowledgements in the release notes).
You are more than welcome to contribute as well:
- star Atrium if you like it
- open a bug or create a feature request
- share your ideas via issue or slack
- ask a question so that we better understand where Atrium needs to improve.
- write a blog post about Atrium (e.g. about a feature you like) or a tutorial (let us know we happily link to your page)
- share your assertion functions with the rest of us by creating a pull request (no need for i18n support or the like, we can augment your pull request).
- have a look at the help wanted issues if you would like to code (ping us on Slack if there are not any).
Please have a look at CONTRIBUTING.md for further suggestions and guidelines.
Sponsors
We would like to thank the following sponsors for their support:
- Tegonal GmbH for sponsoring Support and PR-Review time.
Do you want to become a sponsor as well? Great, have a look at the following GitHub sponsor profiles:
- robstoll (Author and main contributor)
or ping @robstoll in the Slack-Channel if you would like to support the project in another way.
License
Atrium is licensed under EUPL 1.2.
Atrium is using:
- KBox licensed under Apache 2.0
- Niok licensed under Apache 2.0
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