CustomerPresenterTest.kt

@Mock
private lateinit var view: CustomerView
@Mock
private lateinit var usecase: CustomerUsecase
private lateinit var presenter: CustomerPresenter
@Test
fun `should show customer data`() {
    val expectedResponse = mock(CustomerDetail::class.java)
     `when`(usecase.getCustomerData()).thenReturn(Single.just(expectedResponse))
   
    presenter.onResume()

    verify(usecase).getCustomerData()
    verify(view).showLoader()
    verify(view).hideLoader()
    verify(view).populateData(expectedResponse)
}


@Test
fun `should show error when customer response call fails`() {
    `when`(usecase.getDaily()).thenReturn(Single.error(Exception()))

    presenter.onResume()

    verify(usecase).getCustomerData()
    verify(view).showLoader()
    verify(view).hideLoader()
    verify(view).showError()
}
@Test
fun `should show error when network is unavailable`() {
    val res = mock(Resources::class.java)
    `when`(res.getString(R.string.generic_server_error)).thenReturn("Something went wrong")
    `when`(usecase.getCustomerData()).thenReturn(Single.error(NetworkError(Exception(), res)))

    presenter.onResume()

    verify(usecase).getCustomerData()
    verify(view).showLoader()
    verify(view).hideLoader()
    verify(view).showError(ErrorModel(-1, "Something went wrong"))
}