Testing using KoinTest

HomeActivityTest.kt

import ...

@RunWith(AndroidJUnit4ClassRunner::class)
class HomeActivityTest: KoinTest {
    
    @get:Rule
    var intentRule = IntentsTestRule(HomeActivity::class.java, true, false)
    
    lateinit var mockModule: Module
    lateinit var mockedInteractor: HomeInteractor
    
    @Before
    override fun setup() {
        mockedInteractor = Mockito.mock(HomeInteractor::class.java)
        mockedModule = module {
            single(override = true) { mockedInteractor }
        }
        
        loadKoinModules(mockModule)
    }
    
    @After
    override fun tearDown() {
        unloadKoinModules(mockModule)
    }
    
    // Sample test case using the above mocks
    @Test
    fun testApiFailureDisplaysError() {
        // Setting up the mocks
        val testRxSubject = BehaviourSubject.create<Result<String>>()
        `when`(mockedInteractor.getResultFromApi()).thenReturn(testRxSubject)
        
        // Given: Progress is displayed on Home Page launch
        intentRule.launchActivity(null)
        onView(withId(R.id.progressBar)).check(matches(isDisplayed()))
        
        // When: Api throws an error
        testRxSubject.onError(Exception())
        
        // Then: Progress bar should be removed and error text should be displayed.
        onView(withId(R.id.progressBar)).check(matches(not(isDisplayed())))
        onView(withId(R.id.failureTextView))
            .check(matches(isCompletelyDisplayed()))
            .check(matches(withText("Oops, there's some issue, try again later!")))
    }
}