How do I test the fails of a test that relies on a `suspend` funciton? Let's consider this class `...

# multiplatform

[Riccardo Montagnin]

How do I test the fails of a test that relies on a suspend funciton?

Let's consider this class

/**
 * Allows the login of a user based on his private key.
 */
class PerformLoginUseCase internal constructor(private val repository: AuthenticationRepository){

    /**
     * Logs the user into the system using the given [authKey].
     * @return the user data once the login has been successful.
     */
    suspend operator fun invoke(authKey: PrivateKey): UserData {
        return repository.login(authKey)
    }
}

I have the following test

@Test
fun useCaseThrowsExceptionWhenRepositoryDoes() {
    assertFailsWith(Throwable::class) {
        coEvery { repository.login(any()) } throws Throwable()
        GlobalScope.launch { performLogin(mockk()) }
    }
}

While this should work properly, it fails with an assertionError. I think the exception is not raised in time, so who should I do this?

[gildor]

Because you run background job that return immediately and there is no chance for assertFailsWith catch it
It’s like this code, there is no way to catch exception in this case too

assertFailsWith(Throwable::class) {
   thread { error("Some error") }
}

[gildor]

use runBlocking instead of GlobalScope.launch

[gildor]

You shouldn’t use GlobalScope in tests (at least, I don’t see good use cases for this)

[gildor]

and to test suspend functions just use runBlocking (suspend @Test functions are not supported yet, but will be soon)

[Riccardo Montagnin]

It's a common test, and I can't use the runBlocking method inside. I don't know why, but wit hthe following dependencies, it is not included:

implementation deps.kotlin.stdlib.common
implementation deps.kotlinx.coroutines.common
implementation deps.kotlin.test.common
implementation deps.kotlin.test.annotations
implementation deps.kotlinx.coroutines.test

[gildor]

runBlocking is not available in MPP

[gildor]

there are workarounds for this

[gildor]

see this issue
https://youtrack.jetbrains.com/issue/KT-22228

[gildor]

also suspend test functions will be available in 1.3.30

[Riccardo Montagnin]

Thank you very much. Any ETA on Kotlin 1.3.30?

[gildor]

as usual, will be available when will be ready %)

[gildor]

but first EAP already available (not sure tho that KT-22228 is available there)

[Riccardo Montagnin]

Thank you very much!

[gildor]

but anyway, you can workaround it with expect/actual + dynamic type for JS