Android test for LiveData

Question

I have this mock class:

class MockCategoriesRepository implements CategoriesRepository {
        @Override
        public LiveData<List<Category>> getAllCategories() {
            List<Category> categories = new ArrayList<>();
            categories.add(new Category());
            categories.add(new Category());
            categories.add(new Category());
            MutableLiveData<List<Category>> liveData = new MutableLiveData<>();
            liveData.setValue(categories);
            return liveData;
        }
    }

and the test:

@Test
public void getAllCategories() {
    CategoriesRepository categoriesRepository = new MockCategoriesRepository();
    LiveData<List<Category>> allCategories = categoriesRepository.getAllCategories();
}

I want to test List<Category> for empty.

How can I do it? Can I use Mockito for it?

Answer 1

You can do without Mockito, just add the following line to your test:

Assert.assertFalse(allCategories.getValue().isEmpty());

To make it work, you should also add:

testImplementation "android.arch.core:core-testing:1.1.1"

to your app/build.gradle file and also add the following to the test class:

@Rule
public TestRule rule = new InstantTaskExecutorRule();

It is needed because by default LiveData operates on its own thread which comes from the Android dependency (not available on pure JVM environment).

So, the whole test should look like:

public class ExampleUnitTest {

    @Rule
    public TestRule rule = new InstantTaskExecutorRule();

    @Test
    public void getAllCategories() {
        CategoriesRepository categoriesRepository = new MockCategoriesRepository();
        LiveData<List<Category>> allCategories = categoriesRepository.getAllCategories();

        Assert.assertFalse(allCategories.getValue().isEmpty());
    }
}