`@InjectMockKs` can't be used with constructor injection

Hi. Not sure whether to report this as a bug or as a feature request.

I did some searching to see if this issue has already been discussed or raised somewhere, but I couldn’t find anything.

Take the following example test class:

@ExtendWith(MockKExtension::class)
internal class SubjectTest(
    @MockK private val xServiceMock: XService,
    @MockK private val yServiceMock: YService,
) {
    @InjectMockKs
    private lateinit var subject: Subject

    // Test functions here.
}

To avoid having to use the Keyword of Shame, I prefer to use constructor injection for the Class Under Test (Subject) as well, so I try to rewrite it as follows:

@ExtendWith(MockKExtension::class)
internal class SubjectTest(
    @MockK private val xServiceMock: XService,
    @MockK private val yServiceMock: YService,
    @InjectMockKs private val subject: Subject,
) {
    // Test functions here.
}

I would expect this to work the same, but unfortunately this results in the following error:

No ParameterResolver registered for parameter [subject] in constructor...

I’ve tried this with MockK versions 1.12.0 and 1.12.1, and it fails the same way in both.

It would be nice if @InjectMockKs would work through constuctor injection as well. In my opinion, lateinit var is ugly, and I prefer not to use it unless absolutely necessary.

Is there a specific reason why this doesn’t work, like with the @MockK annotations? Or is this a bug?

Thanks.

[Raibaz]

This is indeed an unsupported behavior; MockKExtension does not take into account parameters annotated with @InjectMocks.

It should be possible, though, to handle them in the resolveParameters method and inject the mocks; not sure if parameter order is going to be relevant here (it likely is), so we may need to force the @InjectMocks parameter to be the last one, but it shouldn’t be a big deal.

[Raibaz]

Yes please, that would be amazing! 🙏