Hey folks, Question about kotlin coroutines testing api in 1.6.0 when i should use

val dispatcher = StandardTestDispatcher()
val scope = TestScope(dispatcher)

@Test
fun testFoo() = runTest(dispatcher) {
    // ...
}

vs

val dispatcher = StandardTestDispatcher()
val scope = TestScope(dispatcher)

@Test
fun testFoo() = runTest {
    // ...
}

what if i don’t pass the dispatcher, I know it will default to

StandardTestDispatcher

but wouldn’t be those two different

dispatcher

here? 1. created by runTest 2. created by

dispatcher

property

In the second case, the dispatchers would have different

TestCoroutineScheduler

instances, and so they can't be used in the same test. However, the first case is also incorrect: if you create a

TestScope

explicitly, you also must use the form

scope.runTest

, like

val dispatcher = StandardTestDispatcher()
val scope = TestScope(dispatcher)

@Test
fun testFoo() = scope.runTest {
  ...
}

otherwise, the scope is not checked for leaked coroutines at the end of the test. Alternatively, just don't create anything.

@Test
fun testFoo() = runTest {
  ...
}

will work just fine. Create a scope if you do need to inject a scope somewhere into the entities that you're testing.

thanks for the insights, Thanks for the explanation, So better to not use any custom dispatcher and scope until and unless i need to pass dispatcher or scope to the production class (which we usually do: to inject scope or dispatcher)

You could do that, or just get the dispatcher from the test scope given by

runTest

thanks, will keep in mind