PrefrenceRepositoryTest.kt

  class PreferenceRepositoryTest {


    @get:Rule
    var instantExecutorRule = InstantTaskExecutorRule()

    @Mock
    private lateinit var connectionApiServices: ConnectionApiServices

    private lateinit var preferenceRepository: PrefrenceRepository

    @Before
    fun setUp() {

        MockitoAnnotations.initMocks(this)

        preferenceRepository = PrefrenceRepository(connectionApiServices)
    }


    @Test
    fun `checkConnection on start set liveData to LOADING`() {

        whenever(connectionApiServices.checkConnection()).thenReturn(mock())

        val liveData = preferenceRepository.checkConnection()

        assertEquals(liveData.value, Status.LOADING)
    }

    @Test
    fun `checkConnection successful response set liveData to SUCCESS`() {

        whenever(connectionApiServices.checkConnection()).thenReturn(Calls.response("TestResponse"))

        val liveData = preferenceRepository.checkConnection()

        assertEquals(liveData.value, Status.SUCCESS)
    }


    @Test
    fun `checkConnection failure set liveData to ERROR`() {

        whenever(connectionApiServices.checkConnection()).thenReturn(Calls.failure(IOException()))

        val liveData = preferenceRepository.checkConnection()

        assertEquals(liveData.value, Status.ERROR)
    }
}

Retrofit mock + nhrmann/mockito kotlin(just a wrapper around mockito for kotlin)