test and testIn do not behave consistently

[Antimonit]

I've noticed that if a Flow is canceled "externally" (e.g. a StateFlow that is canceled only when the CoroutineScope it was launched in is canceled) then test and testIn do not behave the same.

While test reports all unconsumed events and fails the test, testIn does not and passes the test.

private val flow = flow {
  emit(1)
  emit(2)
  awaitCancellation()
}

// Throws
//   app.cash.turbine.TurbineAssertionError: Unconsumed events found:
//    - Item(2)
@Test
fun test() = runTest {
  flow.test {
    assertEquals(1, awaitItem())
  }
}

// Passes
@Test
fun testIn() = runTest {
  turbineScope {
    val turbine = flow.testIn(backgroundScope)
    assertEquals(1, turbine.awaitItem())
  }
}

This is not necessarily caused by the backgroundScope as it can be replicated with a custom CoroutineScope() + scope.cancel() or even when canceling the Job the turbine was launched in.

I've figured out this behavior is caused by not handling CancellationException as a special case. From the docs of CancellationException: "It indicates normal cancellation of a coroutine".

[Antimonit]

I've put up a PR that attempts to solve this issue.

I can't say I fully understand the library design and all the consequences this might entail, for example when used with some twisted combination with withTimeout. The library itself does a lot of work to differentiate withTimeout from withTurbineTimeout already and I just don't see that deep.