writing-tests

name	writing-tests
description	Guidelines for writing tests in IntelliJ codebase. Use when creating new test classes or test methods.

Writing Tests

Guidelines for writing tests in IntelliJ IDEA codebase.

For examples, see community/platform/testFramework/junit5/test/showcase/.

Prefer JUnit 5 over JUnit 4

Use JUnit 5 with @TestApplication annotation instead of extending LightJavaCodeInsightFixtureTestCase.

Why JUnit 5:

• Faster: No class hierarchy overhead, shared fixtures via companion objects
• Cleaner: Annotations (@TestDisposable, @RegistryKey) instead of manual setup/teardown
• Flexible: Mix EDT and non-EDT tests in one class, parameterized tests, nested tests
• Better isolation: Each test gets fresh disposables automatically

Shared Fixtures Pattern

Use companion object fixtures shared between all tests:

@TestApplication
internal class MyTest {
  companion object {
    private val projectFixture = projectFixture()
    private val moduleFixture = projectFixture.moduleFixture("src")
  }

  private val project get() = projectFixture.get()
  private val module get() = moduleFixture.get()
}

Lifecycle Hooks

Use JUnit 5 lifecycle annotations for setup and teardown:

@TestApplication
internal class MyTest {
  companion object {
    @JvmStatic
    @BeforeAll
    fun setUpClass() {
      // Once before all tests in class
    }

    @JvmStatic
    @AfterAll
    fun tearDownClass() {
      // Once after all tests in class
    }
  }

  @BeforeEach
  fun setUp() {
    // Before each test method
  }

  @AfterEach
  fun tearDown() {
    // After each test method
  }
}

Note: Prefer @TestDisposable over manual @AfterEach cleanup for resources.

Test Disposables

Use @TestDisposable annotation to inject test-scoped disposables (created before each test, disposed after):

@TestDisposable
lateinit var disposable: Disposable

// Or as parameter
@Test
fun myTest(@TestDisposable disposable: Disposable) { ... }

Registry Values in Tests

Use @RegistryKey annotation instead of Registry.get().setValue():

@Test
@RegistryKey(key = "my.registry.key", value = "true")
fun testWithRegistryEnabled() { ... }

System Properties in Tests

Use @SystemProperty annotation instead of System.setProperty():

@Test
@SystemProperty(propertyKey = "my.property", propertyValue = "value")
fun testWithSystemProperty() { ... }

Running Tests in EDT

Use @RunInEdt annotation to run test methods in EDT:

@TestApplication
@RunInEdt
class MyEdtTest {
  @Test
  fun testInEdt() { ... }
}

// Or for specific methods only
@TestApplication
@RunInEdt(allMethods = false)
class MyTest {
  @Test
  @RunMethodInEdt
  fun testInEdt() { ... }
}

Key Classes

• com.intellij.testFramework.junit5.TestApplication - initializes shared application
• com.intellij.testFramework.junit5.TestDisposable - injects test disposables
• com.intellij.testFramework.junit5.RegistryKey - sets registry values
• com.intellij.testFramework.junit5.SystemProperty - sets system properties
• com.intellij.testFramework.junit5.RunInEdt - runs tests in EDT
• com.intellij.testFramework.junit5.fixture.projectFixture - creates project fixtures
• com.intellij.testFramework.junit5.fixture.moduleFixture - creates module fixtures

Showcase Tests

• JUnit5ProjectFixtureTest.kt - project fixture patterns
• JUnit5DisposableTest.kt - disposable injection
• JUnit5SystemPropertyTest.kt - system property usage
• JUnit5RunInEdtTest.java - EDT execution

Running Tests

To run tests via command line, see TESTING.md.

Quick example:

./tests.cmd -Dintellij.build.test.patterns=*MyTest