Kotlin Multiplatform: How to mock objects in a unit test for iOS

Question

I'm working on a Kotlin-multiplatform (KMP) library for iOS / Android. I have written some unit tests for JVM, for which I use MockK to create spies and mocks, but MockK doesn't support Kotlin native fully yet.

Therefore, I was wondering how others working on KMP projects write unit tests for the iOS platform. An example would be really appreciated.

Answer 1

You can use Mockative to mock interfaces in Kotlin/Native and Kotlin Multiplatform, not unlike how you'd mock dependencies using MockK or Mockito.

Full disclosure: I am one of the authors of Mockative

Here's an example:

class GitHubServiceTests {
    @Mock val api = mock(classOf<GitHubAPI>())

    val service = GitHubService(api)

    @Test
    fun test() {
        // Given
        val id = "mockative/mockative"
        val mockative = Repository(id = id, name = "Mockative")
        given(api).invocation { fetchRepository(id) }
            .thenReturn(mockative)

        // When
        val repository = service.getRepository(id)

        // Then
        assertEquals(mockative, repository)

        // You can also verify function calls on mocks
        verify(api).invocation { fetchRepository(id) }
            .wasInvoked(exactly = once)
    }
}

Spies aren't currently supported, but they are on the roadmap.