Hey, I’m facing a bug in kotlin while testing the ...

# coroutines

[Raed Ghazal]

Hey, I’m facing a bug in kotlin while testing the kotlin.Result
basically in unit tests its getting wrapped twice in a Result, so Result<String> becomes Result<Result<String>>
showing the error

class kotlin.Result cannot be cast to class String

I’m mocking the function like this

coEvery {
    repo.getValues(
        LOCATION,
        DATE
    )
} coAnswers { Result.success(DEFAULT) }

[Joffrey]

What is DEFAULT here?

[Raed Ghazal]

you can think of it as a String, its just the same type as what the function returns

[Raed Ghazal]

a const value of the result

[Raed Ghazal]

class Usecase @Inject constructor(
    private val repo: Repo,
) {

    suspend fun call(
        location: Location,
        currentDate: LocalDate,
        currentTime: LocalTime
    ): Result<String> {
        return repo.getResult()
    }
}

in Test class

@Before
fun setup() {
    coEvery {
        repo.getResult(
            LOCATION,
            DATE
        )
    } coAnswers { Result.success("ToBeReturned") }

    usecase = Usecase(
        repo = repo
    )
}

@Test
fun `test`() = runTest {
    val time = LocalTime.of(0, 0, 0)
    val result = usecase.call(LOCATION, DATE, time)

    Truth.assertThat(result.isSuccess).isTrue()

    result.onSuccess {
        Truth.assertThat(it).isEqualTo("ToBeReturned")
    }

}

[Raed Ghazal]

this basically represent the case

[Raed Ghazal]

so I just tried that instead of mocking, I implemented a fake test repo, and it worked, but apparently with mocking this doesn’t work

found multiple issues open for the same bug
https://youtrack.jetbrains.com/issue/KT-47206
https://github.com/mockk/mockk/issues/485

but they are kind of old

[Joffrey]

It'd be nice if you could share minimal code that reproduces the behaviour you're seeing

[Raed Ghazal]

https://kotlinlang.slack.com/archives/C1CFAFJSK/p1681809451028739?thread_ts=1681809181.562609&amp;cid=C1CFAFJSK

[Joffrey]

☝️ this doesn't compile and doesn't have the Repo class

[ephemient]

another #mockk issue: https://github.com/mockk/mockk/issues/1073

[ephemient]

and more: https://github.com/mockk/mockk/issues/947 https://github.com/mockk/mockk/issues/544

[ephemient]

I'm pretty sure this is entirely a problem with mockk and value classes in general

[Raed Ghazal]

ah, yeah it can be the case,
implementing a fake repo that returns the fake data worked, the data is not going to change each test case so a fake repo works for my case as well

alright then, thanks both!