Blocking Tests

When specifying timeouts in tests, Kotest uses the withTimeout coroutine functions that the Kotlin coroutine library provides. These timeouts are co-operative in nature, and a timeout is detected when a coroutine suspends, resumes, or calls yield.

However when executing blocking code, the thread will be blocked and so the coperative approach will not work. In this scenario we must revert to interrupting the thread using Thread.interrupt or something similar. In order for this interruption to work safely, we must execute the test on a dedicated thread.

Therefore, it is up to the user to signify to Kotest that they want a particular test to execute on a dedicated thread that can be safely used for interruption. We do this by enabling the blockingTest flag in test config.

For example:

class MyBlockingTest : FunSpec() {
  init {

    test("interrupt me!").config(blockingTest = true, timeout = 10.seconds) {
       Thread.sleep(100000000)
    }

    test("uses suspension").config(timeout = 10.seconds) {
      delay(100000000)
    }
  }
}

In the above example, the first test requires the blockingTest flag because it uses a thread blocking operation. The second test does not because it uses a suspendable operation.

note

This feature is only available on the JVM.