Kotlin/Gradle/JUnit starter project

A quick tutorial to bootstrap a Kotlin project using Gradle. Optionally, JUnit can also be added.

1. Create a project

1. Download and install IntelliJ Community, free for Java/Kotlin projects. Alternatively, you can use IntelliJ Ultimate EAP (if available, no subscription is required).
2. Go to “File” ⇀ “New project”. In the wizard:
   a. Pick Kotlin on the left menu;
   b. Write a Name and pick a Location;
   c. Activate “Create Git repository”;
   d. Build system: “Gradle”;
   e. JDK: Pick any JDK. If you’re unsure which to pick, go to “Download JDK” (in the dropdown) and select the latest “Oracle OpenJDK”. If you get a warning, decrease one version because Gradle may not support it yet.
   f. Gradle DSL: Pick “Kotlin” as Gradle DSL. Since we’re using Kotlin, it makes sense that the Gradle DSL is Kotlin.
3. Press “Create”.

2. Setup Git

To ensure you don’t lose your work and can always go back in time, ensure you set up Git — even if only locally.

1. If you haven’t picked “Create Git repository” before, start a new git repository (git init).
2. Create (or edit) a .gitignore file with the following content, and commit all the changes:

/.gradle
/.idea
/build

3. Update Gradle/Kotlin

The IDE wizard doesn’t apply the latest versions of Gradle and Kotlin, so let’s do it manually.

1. Check the latest version on the Gradle releases page.
   Upgrade Gradle to its latest version:
   ./gradlew wrapper --gradle-version=LATEST_GRADLE
2. Check the latest version on the Kotlin releases page.
   Upgrade Kotlin at build.gradle.kts

plugins {
    kotlin("jvm") version "LATEST_KOTLIN"
}

3. You may need to click on the second icon to force a Gradle refresh:

4. You may need to update the toolchain to match your JVM that’s used to run the project:

kotlin {
  jvmToolchain(17)
}

4. Set up JUnit

JUnit gets automatically set up for you. You're supposed to see this at build.gradle.kts:

dependencies {
    testImplementation(kotlin("test"))
}

tasks.test {
    useJUnitPlatform()
}

1. Create a dummy test (src/test/kotlin/DummyTest.kt):

import kotlin.test.Test
import kotlin.test.assertTrue

class TestAmazonCart {
   @Test
   fun `everything is fine`() {
      assertTrue(true)
   }
}

Notice that we’re using the imports from Kotlin Test, which abstract JUnit but are the same.

2. Run it (there’s a ️▶️ near the test) to prove that the JUnit setup is good:

You can also run the tests with ./gradlew test

📝 We’ve used IntelliJ IDEA to create a new Kotlin project. However, there’s an alternative way that relies on Gradle.