Kukumber — Getting started with Cucumber in Kotlin

My team is creating an application in Kotlin. To make development of Cucumber tests easier, we decided to also use Cucumber-jvm with Kotlin instead of Java. Fortunately, it is possible to use cucumber-java8 in Kotlin.

Prerequisites

If you’d like to follow along, make sure you have the following installed:

• JDK
• An IDE; for instance IntelliJ, which I use here.
• Maven

Add dependencies

We use Maven, so we added the following dependencies to our pom.xml:

    <properties>
        <cucumber.version>2.3.1</cucumber.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>io.cucumber</groupId>
            <artifactId>cucumber-java8</artifactId>
            <version>${cucumber.version}</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>io.cucumber</groupId>
            <artifactId>cucumber-junit</artifactId>
            <version>${cucumber.version}</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

Note: The cucumber-junit dependency is added so we can add a JUnit Runner to run our tests, which we will do later. 

If you don’t have Kotlin already configured in your project, you’ll need to add those dependencies also (or have IntelliJ do it for you).

Add a feature file

In our src/test/resources folder we create a new directory and add a .feature file. For this example, we’ll reuse the belly.feature from the cucumber-java-skeleton.

Feature: Belly

  Scenario: a few cukes
    Given I have 42 cukes in my belly
    When I wait 1 hour
    Then my belly should growl

Unfortunately the IntelliJ Cucumber plugin does not (yet) support a link between the steps in our feature file and our step definitions, like it does for Java.

Also, we cannot generate snippets in Kotlin directly. Fortunately there is a work around: we can run the tests to generate snippets in Java 8 lambda style. 

You can run the test from IntelliJ by right-clicking the feature file and selecting “Run ‘Feature:belly’” from the context menu.

When you run the tests, you should get something like the following result:

1 Scenarios (1 undefined)
3 Steps (3 undefined)
0m0.021s


You can implement missing steps with the snippets below:

Given("^I have (\\d+) cukes in my belly$", (Integer arg1) -> {
    // Write code here that turns the phrase above into concrete actions
    throw new PendingException();
});

When("^I wait (\\d+) hour$", (Integer arg1) -> {
    // Write code here that turns the phrase above into concrete actions
    throw new PendingException();
});

Then("^my belly should growl$", () -> {
    // Write code here that turns the phrase above into concrete actions
    throw new PendingException();
});


Process finished with exit code 0

Add Step Definitions

In the src/test/kotlin folder, we add a new Kotlin File/Class, called StepDefs. We only have to write a little Kotlin code in the file:

class StepDefs: En {

    init {
    }
}

Note that our StepDefs implement the cucumber.api.java8.En interface, so we need to import it: import cucumber.api.java8.En

Now, when we copy-paste the generated snippets inside the init{ } block, IntelliJ offers to convert it to Kotlin for us. Once we do, we will also need to import the cucumber.api.PendingException mentioned in the snippets.

Now we have the StepDefs.kt file and we can start implementing the steps, as well as the code to make them pass!

Add JUnit runner

To run our features from a JUnit runner, we’ll need to add one. In the src/test/kotlin folder, we add a new Kotlin File/Class, called RunKukesTest.

Running tests from the command line

To run all tests use

mvn test