Kotlin test junit

Kotlin test junit DEFAULT

JUnit 5 With Kotlin for Java Developers


In this article, we will learn the differences between writing JUnit 5 tests in Kotlin and Java. We will also learn how to configure JUnit 5 in our build script using the Gradle Kotlin DSL.

This article is part of the JUnit 5 Tutorial.

Configuration

We write traditional Gradle build scripts as files using the Groovy DSL. Gradle’s Kotlin DSL provides an alternative syntax for several improvements, such as better content assist and refactoring. The build script written in Kotlin DSL is named .

To write JUnit 5 tests in Kotlin, we first need the artifact as a dependency in file and need to tell to use JUnit platform in the tests.

Basic Functionality

Most of the JUnit 5 functionality works in Kotlin just like it would in Java. Everything works out of the box.

One notable difference is how we can customize the display names of methods displayed in test reports or IDEs.

In Java, we could use the annotation to make the method name readable. However, in Kotlin, we can use backtick identifiers for variables and methods.

Using backticks makes both the code and the test results more readable. Usually, we should not use such method names, but it is quite handy for this purpose.

Lazy Evaluation

JUnit 5 added lazy evaluation of error message using lambdas. Using lambdas avoids constructing expensive error messages unnecessarily.

In Kotlin, if the last parameter of a function accepts a function, it can be rewritten as a lambda expression outside the parentheses.

Compared to Java, this makes the syntax even cleaner when writing assertions in Kotlin.

Assertions

Any JUnit 5 assertions in Java work in Kotlin as well. However, there are a couple of Kotlin specific assertion methods that are more suitable for the language. These assertion methods are top-level functions in the package.

Here is an example of asserting that the code throws an exception. In Java, we would pass a lambda inside of the call. In Kotlin, we can again make this more readable by adding a lambda after the assertion call.

The simpler lambda syntax applies to grouped assertions as well. Grouped assertions make it possible to perform multiple assertions at a time and report failures together.

Like in Java, we can write lambdas inside the call in Kotlin, but the syntax is less verbose.

Compared to Java this is once again a little less verbose and more readable.

Parameterized Tests

There are several ways to write JUnit 5 parameterized tests. Most of these approaches work without any changes in Kotlin as well.

With that in mind, there is a difference when using the annotation. The annotation expects a static method inside the class as the source of the parameters.

To achieve the same in Kotlin, we have to create a companion object and annotate the method with . The annotation will make the method exist as a Java static method.

If we didn’t annotate the method with , we would get the following error.

Using parameterized tests like this is ok but not as convenient as in Java. Another thing to note is that there can be only one companion object per class, so all parameter-providing methods need to be together.

Dynamic Tests

JUnit 5 introduces a new programming model that allows us to generate dynamic tests at runtime by a factory method annotated by the annotation.

Typically we would provide a list of instances. Let’s use the calculator from previous examples.

Each of the dynamic tests would appear as their own tests. However, this is not very clean and has some duplication.

Yet again, there is a way to make this more readable. We can use some functional mapping to remove the duplication.

The functional approach is pretty close to what we did with parameterized tests but with a slightly different syntax.

Nested tests

Nested tests in JUnit 5 allow us to define a hierarchical structure for the tests. Coming from Java, we might expect the following example to work.

Such an example will give us a warning Only non-static nested classes can serve as @Nested test classes. JUnit 5 will not discover any tests for execution.

By default, a nested class in Kotlin is similar to a static class in Java. Only non-static nested classes (i.e. inner classes) can serve as test classes.

The solution is to mark the class as an in Kotlin.

Now JUnit 5 will discover the inner nested test classes and their tests.

Static methods and fields

We already briefly touched on static methods and Kotlin. To make a Kotlin method visible as a Java static method, we have to create a companion object and annotate the method with .

Another possible pitfall is when we have to use static fields. In Java, you make the field , so if you are new to Kotlin, you would expect something like this to work.

However, if we write code like this, we will see an error about the field being private:

The solution is to annotate the field with .

Adding the annotation will expose the Kotlin property as a Java field, and JUnit 5 will now see the field.

Lifecycle Methods

The JUnit 5 lifecycle methods all work in Kotlin as well.

However, the methods annotated with and need to be static by default. The reason is that JUnit 5 creates a new test instance per test method, and there is no other way to share state between all tests.

Luckily, it is possible to create a test instance per class instead in JUnit 5 by annotating the test class with . The lifecycle change removes the requirement for static methods.

Since this now shares instance state between tests, you might need to reset state in or , if your test methods rely on state stored in instance variables. In general, try to avoid writing tests that depend on such state.

Repeatable Annotations

Currently, Kotlin does not support repeatable annotations. Consequently, using multiple extensions or tags for a test is slightly more complicated than in Java.

For example, in Java we can repeat the annotation to give multiple tags to a test.

In Kotlin, however, we cannot have multiple annotations. Instead, we have to use a annotation to wrap the repeated tags.

The same happens with multiple extensions, so we cannot use multiple annotations directly. Instead, we need to wrap the extensions with an annotation.

Summary

Most of the JUnit 5 features work perfectly well in Kotlin, although there are some cases where the syntax is somewhat different than in Java. However, due to the way Kotlin language works, we can often make the code more readable.

The example code for this guide can be found on GitHub.

JUnit 5Kotlin

Arho Huttunen
Arho Huttunen
Software Craftsman

A software professional seeking for continuous improvement. Obsessed with test automation and sustainable development.

Sours: https://www.arhohuttunen.com/junit-5-kotlin/

Best Practices for Unit Testing in Kotlin

Unit Testing in Kotlin is fun and tricky at the same time. We can benefit a lot from Kotlin’s powerful language features to write readable and concise unit tests. But in order to write idiomatic Kotlin test code in the first place, there is a certain test setup required. This post contains best practices and guidelines to write unit test code in Kotlin that is idiomatic, readable, concise and produces reasonable failure messages.

Best Practices for Unit Testing in Kotlin

  • Most of the best practices for unit testing in Java also apply for Kotlin tests.
  • Use JUnit5
  • Test Class Lifecycle
    • Use to avoid the need for static members, which are non-idiomatic and cumbersome in Kotlin.
    • Instead of annotating every class with you can change the default lifecycle with the file.
  • Test Fixtures
    • Reuse one instance of the test class for every test methods (by using )
    • Initialize the required objects in the constructor () or in a field declaration ( is helpful). This way, the fields can be immutable () and non-nullable.
    • Don’t use . It forces us to use or nullable types.
  • Put the test method names in backticks and use spaces.
  • Use inner classes to group the test methods.
  • Mocks
    • Use MockK to create mocks in a convenient and idiomatic way. It can also mock final classes by default.
    • Create mocks only once and reset them in a . This way, you can use fields and achieve better performance.
  • Test Libraries
    • There are so many test libraries. Check them out and make up your own mind.
    • When it comes to assertion libraries, I recommend Kotest‘s matchers. They are powerful, idiomatic and concise.
  • Take advantage of data classes
    • Create a reference object and compare it directly with the actual object using an equality assertion.
    • Use data classes to carry the test data (input and expected output) in a .
  • Helper Functions
    • Write helper functions with default arguments to easily create instances with a complex structure.
    • Helper extension functions are useful to concisely create frequently used values (like , )
    • Test-specific extension functions are useful to extend libraries in an idiomatic way to remove distractions in the test code.

At the KotlinConf 2018, I held a talk about this topic. You can watch the video here. Please note that the blog post below is more up to date than the recording. For instance, I now recommend the Kotest matchers instead of AssertJ.

Most of the best practices for unit testing in Java are still valid because they are language-agnostic.

Let’s recap a few points about idiomatic Kotlin code:

  • Immutability. We should use immutable references with instead of .
  • Non-Nullability. We should favor non-nullable types () over nullable types ().
  • No access. It impedes proper object-oriented design, because static access harms testability (can’t exchange objects easily) and obfuscates dependencies and side-effects. Kotlin strongly encourages us to avoid access by simply not providing an easy way to create members.

But how can we transfer these best practices to our test code?

In JUnit4, a new instance of the test class is created for every test method. So the initial setup code (that is used by all test methods) must be static. Otherwise, the setup code would be re-executed again and again for each test method. In JUnit4, the solution is to make those members static. That’s ok for Java as it has a keyword. Kotlin doesn’t have this direct mean - for good reasons because static access is an anti-pattern in general.

Fortunately, JUnit5 provides the annotation. This way, a single instance of the test class is used for every method. Consequently, we can initialize the required objects once and assign them to normal fields of the test class. This happens only once because there is only one instance of the test class.

First, this approach is more concise, because we don’t have to wrap everything into a containing annotated fields. Second, it’s idiomatic Kotlin code as we are using immutable non-nullable references and can get rid of the nasty . Please note, that Kotlin’s is really handy here. It allows object initialization and configuration without a constructor. But using a constructor or an initializer block () is sometimes more appropriate if the initialization code is getting more complex.

In fact, we don’t need JUnit5’s (the equivalent of JUnit4’s ) anymore because we can utilize the means of object-oriented programming to initialize the test fixtures.

Side note: For me, the re-creation of a test class for each test method was a questionable approach anyway. It should avoid dependencies and side-effects between test methods. But it’s not a big deal to ensure independent test methods if the developer pays attention. For instance, we should not forget to reset or reinitialize fields in a block and don’t (re-)assigned fields in general - which is not possible when we use fields. ;-)

Writing on every test class explicitly is cumbersome and easy to forget. Fortunately, we can set the default lifecycle for the whole project by creating the file with the content:

  • Put the test method name in backticks. This allows spaces in the method name which highly improves readability. This way, we don’t need an additional annotation.
  • JUnit5’s is useful to group the test methods. Reasonable groups can be certain types of tests (like , ) or one group for each method under test ( and ).
Readable and Grouped Tests Results in IntelliJ IDEA

Due to the variety of available Kotlin test libraries we are spoilt for choice. Here is an incomplete overview of some Kotlin-native and Java libraries for testing, mocking and assertions (note that some libraries fit into multiple categories):

For me, it’s a matter of taste. Check them out and make up your own mind. We ended up using plain JUnit5, MockK, and Kotest’s matchers.

Kotest for Assertions

For a long time, we still used the powerful AssertJ in our Kotlin projects and it’s still a good choice. But we moved to Kotest‘s matchers. Kotest has the advantage of being written in Kotlin. So it can leverage Kotlin’s language features which allows you to write more idiomatic and concise assertions.

But Kotest is not only an assertion library; it’s a whole test framework. However, I still prefer JUnit5 (for now) due to its simplicity and the better tooling in the IDE. Fortunately, you can use Kotest’s matchers in isolation as they are located in a dedicated dependency.

Final By Default

Classes and therefore methods are final by default in Kotlin. Unfortunately, some libraries like Mockito are relying on subclassing which fails in these cases. What are the solutions to this?

  • Use interfaces
  • the class and methods explicitly for subclassing
  • Enable the incubating feature of Mockito to mock final classes. For this, create a file with the name in with the content .
  • Use MockK instead of Mockito/Mockito-Kotlin. It supports mocking final classes by default.

Use MockK

I highly recommend using MockK. First, you don’t have to worry any longer about final classes or additional interfaces. Second, MockK provides a convenient and idiomatic API for writing mocks and verifications.

Note the usage of lambdas in to nicely group verifications. Moreover, MockK provides reasonable error messages containing all tracked calls if verification fails. I also like that MockK fails with an exception if an unspecified method is called on a mock (strict mocking by default). So you don’t run into mysterious NullPointerExceptions known from Mockito.

Besides, MockK’s relaxed mocks are useful if the class under test uses a certain object, but you don’t want to define the behavior of this mock because it’s not relevant for the test. A relaxed mock returns dummy objects containing empty values.

But mind, that relaxed mocks can also lead to tricky errors, when you forget to mock a required method. I recommend using strict mocks by default and relaxed ones only if you really need it.

Create Mocks Once

Recreating mocks before every test is slow and requires the usage of . So the variable can be reassigned which can harm the independence of each test.

Instead, create the mock instance once and reset them before or after each test. It’s significantly faster (2 s vs 250 ms in the example) and allows using immutable fields with .

The presented create-once-approach for the test fixture and the classes under test only works if they don’t have any state or can be reset easily (like mocks). In other cases, re-creation before each test is inevitable.

Data Classes for Assertions

Single Objects

If possible don’t compare each property for your object with a dedicated assertion. This bloats your code and - even more important - leads to an unclear failure message.

This leads to poor failure messages:

? What is the semantics of the numbers? Design id or User id? What is the context/the containing class? Hard to say.

Instead, create an instance of the data classes with the expected values and use it directly in a single equality assertion.

This way, we get a nice and descriptive failure message:

We take advantage of Kotlin’s data classes. They implement and out of the box. So the equals check works and we get a really nice failure message. Plus, Kotest detects data classes and outputs the property that is different. Moreover, by using named arguments, the code for creating the expected object becomes very readable.

Lists

We can take this approach even further and apply it to lists. Here, Kotest’s powerful list assertions are shining.

How cool is that?

Other Useful Kotests Assertions

Usually, comparing all properties of a data class is what you need in the test. But from time to time, it’s useful to ignore some properties or to compare only some properties.

Group Assertions With Kotest’s

If you really want to assert only a few properties of a data class, consider grouping the assertions using Kotest’s function. First, it nicely groups the code. Second, failure messages will also print the object that was invoked on. That provides very useful context.

Data Classes for Parameterized Tests

Data classes can also be used for parameterized tests. Due to the automatic implementation, we get a readable test result output in IDEA and the build.

If we use data classes as test parameters we get readable test results

Use Helper Functions with Default Arguments to Ease Object Creation

In reality, data structures are complex and nested. Creating those objects again and again in the tests can be cumbersome. In those cases, it’s handy to write a utility function that simplifies the creation of the data objects. Kotlin’s default arguments are really nice here as they allow every test to set only the relevant properties and don’t have to care about the remaining ones.

This leads to concise and readable object creation code.

  • Don’t add default arguments to the data classes in the production code just to make your tests easier. If they are used only for the tests, they should be located in the test folder. So use helper functions like the one above and set the default arguments there.
  • Don’t use just to ease object creation. Extensive usage is hard to read; especially with nested structures. Prefer the helper functions.
  • Locate all helper functions in a single file like . This way, we can reuse the functions like lego bricks for each test.

Helper Extension Functions for Frequently Used Values

I prefer to use fixed values instead of randomized or changing values. But writing code like again and again is annoying and blows the code.

Fortunately, we can write extension functions for frequently used objects like , or MongoDB’s .

The code will become concise while keeping the different values visible:

The failure messages can be easily traced back to the test code:

Test-Specific Extension Functions

Extension Functions can be useful to extend an existing library in a natural way. Here is an example: Kotest’s for floating comparison requires a tolerance parameter. This leads to a lot of code duplication, bloated code, and distraction while reading the tests.

Instead, define the extension function on which delegates to a invocation with a fixed tolerance. This method is specific for the current test class and can be placed there.

The essential test logic becomes clearer and the code is still idiomatic as we stick to the pattern of Kotest.

The same technique can be used for all libraries with a fluent API.

Testcontainers is a Java API to control containers within your test code. That’s great for executing your tests against a real database instead of an in-memory database. I highly recommend this approach. However, starting a new container for each test is usually a big waste of time. It’s better to create the container once and reuse it for every test. Kotlin’s singletons and lazy initialized properties () are very helpful here.

  • This way, we don’t need any test framework integration (like a JUnit5 extension for Testcontainers).
  • Don’t forget to clean up the database before each test method using a method.
  • Be careful when you are running the tests in parallel. Consider using different “database names” (or “schema” in case of RDBs) for each test class to avoid side-effects.
  • I highly recommend the book Kotlin in Action by Dmitry Jemerov and Svetlana Isakova
Sours: https://phauer.com/2018/best-practices-unit-testing-kotlin/
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On the mysteries of kotlin.test

If you’ve ever asked questions like the following, read on:

  • Is there a connection betweenkotlin.test and KotlinTest (since renamed to Kotest)?
  • What are the kotlin-test and kotlin-test-junit dependencies that gradle init generates?
  • How do I switch kotlin.test from using JUnit4 to using JUnit5? What’s all this nonsense and, more importantly, why is any of it necessary?
  • What are junit.jupyter.engine and junit.jupyter.api? Why do I need them, when do I need them, and why do I seem to only need them sometimes?
  • Why do I keep getting “Test events were not received” in IDEA? Why do I sometimes get test results on one run, only to get “Test events were not received” on the next one?
  • Why don’t I get any test results when running tests from the command line, even though I get them when running in IDEA?

To answer all of these question in a satisfying way, we’ll first talk briefly about some fundamental testing topics that will be mentioned throughout the article. After that, we’ll dispel a misconception that can be a real gotcha for beginners.

We’ll then go on to dissect the kotlin.test library module by module and explain the roles each of them play. We’ll then proceed to take a detailed look at why two of the modules that target a different version of the same tool (JUnit4 vs. JUnit5) require very different configurations, and use that to gain some insight into how things work under the hood.

Finally, we’ll finish things off by showing you how to configure Gradle to show output in the console, and give a quick tip on what to do when, sporadically, tests don’t seem to run.

Some basic things first

Before we start, we need to clarify some terminology. I recommend reading this short article that introduces the topic nicely, but TL; DR, it is important to distinguish between:

  • a test framework & assertion library (which can be part of the test framework), which is what provides you with the API (functions, annotations, etc.) you use to write the actual tests, and
  • a test runner, which is what takes those tests, runs them and collects the results, possibly generating various reports along the way or offering additional features

Another term you need to be familiar with is JUnit. JUnit is a testing tool for Java that’s part of a collection of testing tools collectively known as XUnit and it provides all of the capabilities described above (i.e. it offers both a test framework, assertions and test runner).

It’s important to distinguish between JUnit4 and JUnit5. JUnit5 is different from JUnit4 in many ways, but key among them is that it provides a platform that can be used by other testing frameworks to run their tests on the JVM. Basically, any (JVM-based) test library can take advantage of this and delegate the task of running the tests (the test runner part) to JUnit, instead of implementing it itself. An example of a library that does this is KotlinTest.

If you’re interested in learning more about the JUnit5 architecture, Nicolai Parlog wrote an excellent article about this topic.

kotlin.test vs. KotlinTest (now known as Kotest)

The first important thing to understand about kotlin.test (i.e. the library you’ll find in the Kotlin reference) is that, as far as I know, it has absolutely nothing to do with the library KotlinTest.

In retrospect, it’s fairly obvious — for instance, you can clearly see it from the completely different namespaces of both libraries (kotlin.test vs. io.kotlintest, currently io.kotest). But when I was starting out and knew nothing about the Kotlin ecosystem, I was confused by the almost identical names, the fact that one would always pop up when googling for the other and the very similar API (specifically the shouldBe in kotlin.test vs the shouldBe in KotlinTest). I’m actually almost embarrassed to admit how long it took before it even occurred to me that they might not be the same thing (months), although it seem like I’m not the only one who made a similar mistake.

Since this article was published, the KotlinTest library has been renamed to Kotest for precisely this reason.

The library kotlin.test is basically a part of the Kotlin language (in the same sense that stdlib or reflect are) that came into existence at the end of 2015, while KotlinTest was started about a month later and as far as I can tell, has no affiliation with Jetbrains (although another Kotlin testing library, Spek, does come from JetBrains).

Interestingly, it seems the API of kotlin.test is scheduled to be removed completely in Kotlin 1.4.

Understanding the modules in kotlin.test

The main purpose of kotlin.test is to provide a unified API for writing tests regardless of the test runner and assertion library used. This is especially useful for multiplatform projects, as it allows you to write tests for e.g. JavaScript using the same API you would use the write the tests when targeting the JVM.

This is achieved by abstracting away basic assertion logic into an Asserter interface and some basic annotations (such as ) and then providing implementations for different test frameworks/runners, such as JUnit or TestNG .

The definitions of the interface and basic assertion methods (such as ) are in kotlin-test-common, while kotlin-test-annotations-common contains the basic annotations. The annotations are defined with , i.e. they are not actually implemented there.

The framework specific modules (kotlin-test-junit etc.) provide implementations of the interface in the context of the corresponding test framework, and provide implementations of the annotations.

This leaves the kotlin-test module. There’s slight confusion caused by the fact that in the repo, it’s actually found under the jvm folder(the module name is passed as an argument to the compiler).

This module includes the default Asserter implementation that is mentioned in the reference, which, from what I could tell, it’s only used in internal tests of the library. Other than that, it really doesn’t do much other than implement some common functionality used by the JVM framework specific modules (junit, junit5 & testng). A lot of the functionality it provides is marked as deprecated and either scheduled for removal or provided for binary compatibility.

As an interesting side-note, even though (as of Gradle 6.0.1) gradle init includes the kotlin-test module, you don’t actually need to do that, because all of the framework-specific modules include it transitively (see the build.gradle files in the respective modules).

kotlin-test-junit vs. kotlin-test-junit5

Running gradle init under Gradle 6.0.1 generates a build.gradle with kotlin-test and kotlin-test-junit included as testImplementation dependencies, which sets up kotlin.test with the JUnit4 runner. You can take a look at the slightly beautified code here.

If you want to switch to JUnit5, the process is not as simple as you might think — just changing the second dependency to kotlin-test-junit5 doesn’t do the trick and instead causes the test task to run without anything happening (in IDEA, you get a Test events were not received message).

After some googling, you will most likely come up with the following two-step solution:

  1. Add org.junit.jupiter:junit-jupiter-api and org.junit.jupiter:junit-jupiter-engine to the dependencies
  2. Configure Gradle to use JUnit5:
tasks {
test {
useJUnitPlatform()
}
}

But why? Why do you need extra dependencies for JUnit5, when JUnit4 works out of the box? Why do you need additional configuration for JUnit5 when, again, JUnit4 works out of the box? Well, as one article puts it, “it is the way”, but that doesn’t really satisfy anybody. To answer those questions, we’ll need to understand the difference in the architecture of JUnit4 vs. JUnit5, as well as take a look at the build.gradle files of kotlin-test-junit and kotlin-test-junit5.

We already talked about the architectural differences — basically, JUnit4 is a monolith, with everything included in a single module, while JUnit5 is split into multiple submodules, with the logic that recognizes and runs the tests (the runner, called a in JUnit parlance) iseparated from the API that allows you to write them (the test framework & assertion library).

This is precisely what those two dependencies are: jupiter-api gives you the tools you need to write the tests, while jupiter-engine allows you to run them. This also explains why the former is included with a testImplementation directive, while the latter with a testRuntimeOnly.

If you look at the build.gradle file of kotlin-test-junit5, you’ll see that the jupiter-api dependency is also being included (it has to be, otherwise kotlin.test couldn’t map its annotations/Asserter interface to the JUnit5 world), so in fact, all you really need to include is the jupiter-engine dependency.

Since JUnit 5.4, it’s even easier — just include the new org.junit.jupiter:junit-jupiter artifact. That’s it.

So why does kotlin-test-junit work without any additional dependencies? The answer lies in its build.gradle file — the junit:junit dependency, which contains all of JUnit4, is being included transitively, much like jupiter-api.

So to sum up — for kotlin.test to work, a runner always has to be included in the dependencies. With JUnit4, the runner is bundled with the code used to actually implement kotlin-test-junit, so it get’s included transitively. With JUnit5, it’s decoupled, and only the API is included transitively, so the runner needs to be included separately.

To the second point, the call to is used to configure Gradle to actually use whichever test runner you decided on using, be it JUnit4 (), JUnit5 () or TestNG ().

As a nice demonstration of the power of kotlin.test, you can try switching from JUnit to TestNG. Simply change the kotlin-test-junit dependency to kotlin-test-testng and call in the configuration block and it all just works.

If you then look at the dependencies, either through the dependencies task, or in the build.gradle file, you’ll see the org.testng.testng dependency, which is (similarly to JUnit) a monolith containing both the TestNG API and the TestNG runner.

Why does JUnit4 work without any additional configuration? Because if none is specified, JUnit4 is selected by default.

Configuring console output

Even after you have done all this, you’ll notice a final weird quirk: while running the tests in IDEA works fine, if you run the task through the Gradle Wrapper directly (./gradlew test), nothing will seem to happen. What actually happens is that the tests run (you might even see a quick flash on the screen), but no output gets sent to the console.

To remedy that, configure Gradle to log test events to the console:

import org.gradle.api.tasks.testing.logging.TestLogEventtasks {
test {
testLogging {
events = setOf(
TestLogEvent.STARTED,
TestLogEvent.PASSED,
TestLogEvent.FAILED
)// show standard out and standard error of the test
// JVM(s) on the console
showStandardStreams
= true
}
}
}

is an enum (don’t forget to import it), so if you want to log all events, use .

There’s more you can do, and Łukasz Wasylkowski wrote an excellent article demonstrating the possibilities. The article targets Groovy, but it shouldn’t be too hard to translate.

Check out this article in the Gradle manual for some help, or leave a note in the comments and I’ll try to help out.

Tests randomly not being run

From time to time, tests appear not to run, even though you swear they did just a moment ago.

This will actually happen whenever you run the test task more than once in a row, without first making a change to the files or running the clean task. It makes sense — no need to run tests if nothing has changed — but if you’re not expecting it, it can be confusing before you figure it out.

Sours: https://levelup.gitconnected.com/on-the-mysteries-of-kotlin-test-444cf094e69f
JUnit 5 with Kotlin for Java Developers

Test code using JUnit in JVM – tutorial

This tutorial will show you how to write a simple unit test and run it with the Gradle build tool.

The example in the tutorial has the kotlin.test library under the hood and runs the test using JUnit.

To get started, first download and install the latest version of IntelliJ IDEA.

Add dependencies

  1. Open a Kotlin project in IntelliJ IDEA. If you don't already have a project, create one.

    Specify JUnit 5 as your test framework when creating your project.

  2. Open the file and add the following dependency to the Gradle configuration. This dependency will allow you to work with and :

    dependencies { // Other dependencies. testImplementation(kotlin("test")) }

    dependencies { // Other dependencies. testImplementation 'org.jetbrains.kotlin:kotlin-test' }

  3. Add the task to the file:

    tasks.test { useJUnitPlatform() }

    test { useJUnitPlatform() }

    If you created the project using the Project Wizard, the task will be added automatically.

Add the code to test it

  1. Open the file in .

    The directory contains Kotlin source files and resources. The file contains sample code that will print .

  2. Create the class with the function that adds two integers together:

    class Sample() { fun sum(a: Int, b: Int): Int { return a + b } }

Create a test

  1. In IntelliJ IDEA, select Code | Generate | Test... for the class.

    Create a test
  2. Specify the name of the test class. For example, .

    IntelliJ IDEA creates the file in the directory. This directory contains Kotlin test source files and resources.

    You can also manually create a file for tests in .

  3. Add the test code for the function in :

    • Define the test function using the @Test annotation.

    • Check that the function returns the expected value by using the assertEquals() function.

    import kotlin.test.Test import kotlin.test.assertEquals internal class SampleTest { private val testSample: Sample = Sample() @Test fun testSum() { val expected = 42 assertEquals(expected, testSample.sum(40, 2)) } }

Run a test

  1. Run the test using the gutter icon.

    Run the test

    You can also run all project tests via the command-line interface using the command.

  2. Check the result in the Run tool window:

    Check the test result. The test passed successfully

    The test function was executed successfully.

  3. Make sure that the test works correctly by changing the variable value to 43:

    @Test fun testSum() { val expected = 43 assertEquals(expected, classForTesting.sum(40, 2)) }

  4. Run the test again and check the result:

    Check the test result. The test has been failed

    The test execution failed.

What's next

Once you've finished your first test, you can:

Last modified: 08 September 2021

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Sours: https://kotlinlang.org/docs/jvm-test-using-junit.html

Junit kotlin test

kotlin.test

The library provides annotations to mark test functions and a set of utility functions for performing assertions in tests, independently of the test framework being used.

The test framework is abstracted through the Asserter class. A basic implementation is provided out of the box. Note that the class is not intended to be used directly from tests, use instead the top-level assertion functions which delegate to the .

The library consists of the modules:

  • – assertions for use in common code;
  • – test annotations for use in common code;
  • – a JVM implementation of assertions from ;
  • – provides an implementation of Asserter on top of JUnit and maps the test annotations from to JUnit test annotations;
  • – provides an implementation of Asserter on top of JUnit 5 and maps the test annotations from to JUnit 5 test annotations;
  • – provides an implementation of Asserter on top of TestNG and maps the test annotations from to TestNG test annotations;
  • – a JS implementation of common test assertions and annotations with the out-of-the-box support for Jasmine, Mocha, and Jest testing frameworks, and an experimental way to plug in a custom unit testing framework.

Packages

Index

All Types
Sours: https://kotlinlang.org/api/latest/kotlin.test/
Android Unit Test Tutorial - Writing Your First Unit Test

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