Hey folks, Question about kotlin coroutines testin...

# coroutines

[samp]

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

[Dmitry Khalanskiy [JB]]

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.

[samp]

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)

[samp]

@Dmitry Khalanskiy [JB]

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.

what if i need to pass dispatcher to the entities? In that case, do you suggest to create an explicitly create a dispatcher and use that dispatcher to run the test like: runTest(dispatcher) and pass that dispatcher to the entities as well?

[Joffrey]

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

[samp]

thanks, will keep in mind