Hello! I tried to mockk a kotlin `flow` so I can bypass one line of code in my class. Basically I ne...

# mockk

[Mikolaj]

Hello!
I tried to mockk a kotlin flow so I can bypass one line of code in my class. Basically I need to bypass the dropWhile method so it passes the values in flow to the next method. I tried to create mock like that:

@Test
    fun `test mock flow`() = runTest {
        val flow: Flow<Int> = mockk(relaxed = true) {
            coEvery { dropWhile(any()) } returns this
        }
    }

But then i get error Failed matching mocking signature for left matchers: [any()] . Is it possible to create a mock that will bypass the dropWhile method?

Thanks!

[Jakub Gwóźdź]

dropWhile is an extension function, see here for tips: https://mockk.io/#extension-functions

[Jakub Gwóźdź]

(also, it’s not suspending, so every {… instead of coEvery should be enough, I think

[Jakub Gwóźdź]

this works for me:

@Test
    fun `test mock flow`(): Unit = runBlocking {
        val flow: Flow<Int> = flowOf(1, 2, 1, 3, 1, 4)
        mockkStatic(Flow<Int>::dropWhile)
        every { flow.dropWhile(any()) } answers { println("mock hit!"); flow }
        flow.dropWhile { it < 3 }.collect { println(it) }
    }

(also, thanks for the puzzle, I clearly needed a distraction 🙂 )

[Mikolaj]

Thanks! That helped on the JVM side of things. Unfortunately since I'm using KMM I can not mock KFunction using mockkStatic 😕 but that is entirely different problem and Your solution for mocking the flow works! 😄

[Jakub Gwóźdź]

outside JVM, mockkStatic("kotlinx.coroutines.flow.FlowKt") should work

[Mikolaj]

Yes it does 😄 Thank you very much for Your help