Kotlin Multiplatform test interceptors with Burst

Last year we announced Burst, our Kotlin Multiplatform library for parameterized tests.

I recently needed another JUnit feature that’s absent on Kotlin/Multiplatform: test rules! They offer a simple way to reuse behavior across tests. Here’s some of my favorites:

• Paparazzi is Cash App’s snapshot testing for Android. The library’s main entry point is a test rule.
• MockWebServer is an HTTP server focused on testing HTTP clients. A major contributor to OkHttp’s stability is its MockWebServer-powered test suite!
• JUnit’s Timeout rule lets me write difficult integration tests without the risk of hanging my test suite.

JUnit rules don’t work on non-JVM platforms, so with Burst 2.8 we’re introducing a Kotlin Multiplatform alternative called TestInterceptor. It’s straightforward to create one:

class TemporaryDirectory : TestInterceptor {
  lateinit var path: Path
    private set

  override fun intercept(testFunction: TestFunction) {
    path = createTemporaryDirectory(testFunction)
    try {
      testFunction()
    } finally {
      deleteTemporaryDirectory(path)
    }
  }
}

Use @InterceptTest to apply it:

class DocumentStorageTest {
  @InterceptTest
  val temporaryDirectory = TemporaryDirectory()

  @Test
  fun happyPath() {
    DocumentWriter().write(SampleData.document, temporaryDirectory.path)
    val decoded = DocumentReader().read(temporaryDirectory.path)
    assertThat(decoded).isEqualTo(SampleData.document)
  }
}

Burst can also intercept suspending tests with CoroutineTestInterceptor. JUnit rules can’t do that!

Get Burst on GitHub.