How to unit test Retrofit api calls?

I test my Retrofit callbacks using Mockito, Robolectric and Hamcrest libraries.

First of all, set up lib stack in your module's build.gradle:

dependencies {    testCompile 'org.robolectric:robolectric:3.0'    testCompile "org.mockito:mockito-core:1.10.19"    androidTestCompile 'org.hamcrest:hamcrest-library:1.1'}

In jour project's global build.gradle add following line to buildscript dependencies:

classpath 'org.robolectric:robolectric-gradle-plugin:1.0.1'

Then enter "Build Variants" menu in Android Studio (to quickly find it, hit Ctrl+Shift+A and search for it), and switch "Test Artifact" option to "Unit Tests". Android studio will switch your test folder to "com.your.package (test)" (instead of androidTest).

Ok. Set-up is done, time to write some tests!

Let's say you've got some retrofit api calls to retrieve a list of objects that need to be put into some adapter for a RecyclerView etc. We would like to test whether adapter gets filled with proper items on successful call.To do this, we'll need to switch your Retrofit interface implementation, that you use to make calls with a mock, and do some fake responses taking advantage of Mockito ArgumentCaptor class.

@Config(constants = BuildConfig.class, sdk = 21,    manifest = "app/src/main/AndroidManifest.xml")@RunWith(RobolectricGradleTestRunner.class)public class RetrofitCallTest {    private MainActivity mainActivity;    @Mock    private RetrofitApi mockRetrofitApiImpl;    @Captor    private ArgumentCaptor<Callback<List<YourObject>>> callbackArgumentCaptor;    @Before    public void setUp() {                    MockitoAnnotations.initMocks(this);        ActivityController<MainActivity> controller = Robolectric.buildActivity(MainActivity.class);        mainActivity = controller.get();        // Then we need to swap the retrofit api impl. with a mock one        // I usually store my Retrofit api impl as a static singleton in class RestClient, hence:        RestClient.setApi(mockRetrofitApiImpl);        controller.create();    }    @Test    public void shouldFillAdapter() throws Exception {        Mockito.verify(mockRetrofitApiImpl)            .getYourObject(callbackArgumentCaptor.capture());        int objectsQuantity = 10;        List<YourObject> list = new ArrayList<YourObject>();        for(int i = 0; i < objectsQuantity; ++i) {            list.add(new YourObject());        }        callbackArgumentCaptor.getValue().success(list, null);        YourAdapter yourAdapter = mainActivity.getAdapter(); // Obtain adapter        // Simple test check if adapter has as many items as put into response        assertThat(yourAdapter.getItemCount(), equalTo(objectsQuantity));    }}

Proceed with the test by right clicking the test class and hitting run.

And that's it. I strongly suggest using Robolectric (with robolectric gradle plugin) and Mockito, these libs make testing android apps whole lotta easier.I've learned this method from the following blog post. Also, refer to this answer.

Update: If you're using Retrofit with RxJava, check out my other answer on that too.

If you use .execute() instead of .enqueue() it makes execution synchron, thus the tests can ran properly without the need of importing 3 different libraries and adding any code or modify the build variants.

Like:

public class LoginAPITest {    @Test    public void login_Success() {        APIEndpoints apiEndpoints = RetrofitHelper.getTesterInstance().create(APIEndpoints.class);        Call<AuthResponse> call = apiEndpoints.postLogin();        try {            //Magic is here at .execute() instead of .enqueue()            Response<AuthResponse> response = call.execute();            AuthResponse authResponse = response.body();            assertTrue(response.isSuccessful() && authResponse.getBearer().startsWith("TestBearer"));        } catch (IOException e) {            e.printStackTrace();        }    }}

• The JUnit framework never executes the code in the CallBack functions because the main thread of execution terminates before the response is retrieved. You can use CountDownLatch as shown below:

  @Testpublic void testApiResponse() {    CountDownLatch latch = new CountDownLatch(1);    mApiHelper.loadDataFromBackend(new Callback() {        @Override        public void onResponse(Call call, Response response) {            System.out.println("Success");            latch.countDown();        }        @Override        public void onFailure(Call call, Throwable t) {            System.out.println("Failure");            latch.countDown();        }    });    try {        latch.await();    } catch (InterruptedException e) {        e.printStackTrace();    } }

• This test sample may be helpful too.

• My advice isn't to perform testing for the API responses in the android app. There are many external tools for this.