用Kotlin写测试代码的几个坑

Write Unit Test in Kotlin

Latest Android Studio(3.0 Canary 7) allow us to use Kotlin to write source code and test case too. I’ve written a post about how to test kotlin code in java unit test files. Today, I want to talk about how to test kotlin code in kotlin. And it is not as that easy as you might think.

1. Mock

We’ve written the following java test code many many times:

public FooTest {
    @Mock private IView view;
    
    @Before public void setUp(){
        MockictoAnnotation.init(this);
    }
}

But this does not work in kotlin. Kotlin does not allow you declare a field without giving it a value. In this case, view filed should be assigned a value, which is impossible for us. We can not initialize it until the setUp() method is invoked.

So the lateinit value is here to rescue us

public FooTest {
    @Mock lateinit var view: IView
    
    @Before public void setUp(){
        MockictoAnnotation.init(this);
    }
}

2. init again

Now we want to test a presenter. Still we can not just use private Presenter presenter in kotlin. Besides, the initialization of presenter depends on the view field in the code above.

Here is what we do

public FooTest {
    @Mock lateinit var view: IView
    var presenter : Presenter by lazy {
        Presenter(view)
    }
    
    @Before public void setUp(){
        MockictoAnnotation.init(this);
    }
}

3. static import

Kotlin does not support features like “static import”, which is used very frequently in the test case. You must see a lot of onView().perform().check(), or assertEquals(), or any(***Class), or `mock(***Class) and so on.

Now since we cannot use static import, we have to use the boring Mockito.mock()

But not be frustrated, we still have a way to achieve the static import effect by do this:

import org.mockito.Mockito.*
…
val ids = longArrayOf(9517717L)
verify(view).jumpToDetilsPage(9517717, ids)

4. Robolectric

Some test cases need Robolectric to test some special class. But since the Class object is different between Java and Kotlin.

We may have a little confused about how to import Robolectric. Just like the screenshot below:

Here is what we do:

@RunWith(RobolectricTestRunner::class)
@Config(constants = BuildConfig::class, sdk = intArrayOf(Build.VERSION_CODES.LOLLIPOP))
class PresenterTest {