Android robolectric – how to simulate and inject business classes when creating activity objects

My task is to write unit tests for existing Android activities, and I haven't written code that conforms to unit tests (tight coupling)

Scenario: I have a stroagemanager class, which is instantiated in myactivity oncreate method

@Override
protected void onCreate(Bundle savedInstanceState) 
{            
 StorageManager storagemanager = GetStorageManager(); // return new object of stroage manager
 super.onCreate(savedInstanceState);.....
    ...
}

In order to create an activity instance through robolectric, I need to simulate myactivity before setting it in the test

Question: how to simulate and inject a myactivity object when it is created through robolectric

Note: This is an existing activity. I don't have much freedom to modify the activity code for large-scale expansion. In addition, we are using the mockito framework for simulation, so it would be great if you use mockito for examples

This is the sample code I tried to use robolectric in mockito, but it didn't work properly:

@RunWith(RobolectricTestRunner.class)
public class myActivityTest {

    @Mock
    private StorageManager storageManager;

    @InjectMocks
    MyActivity myActivity;

    @Before
    public void setUp() {
        ActivityController<MyActivity> activityController = Robolectric.buildActivity(MyActivity.class);
        myActivity = activityController.get();
       // when(registrationActivity.GetMetricManager()).thenReturn(mock(MetricsManager));
        initMocks(this);
        activityController.setup();         
    }

}

I have tried the following suggested solution, but now this error occurs:

I have modified my code according to your suggestion and threw the following error. When executing this line, activitycontroller activitycontroller = robolectric. Buildactivity (testmyactivity. Class);

java.lang.RuntimeException：java.lang.NoSuchMethodException：Tests $TestMyActivity.()

at org.robolectric.util.ReflectionHelpers.callConstructor(ReflectionHelpers.java:233)
    at org.robolectric.util.ActivityController.of(ActivityController.java:27)
    at org.robolectric.Robolectric.buildActivity(Robolectric.java:42)
    at  Tests$TestMyActivity.setUp(RegistrationTest.java:89)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:24)

resolvent:

First, storagemanager is not a field or a field passed by constructor, so @ injectmocks has no effect

I will refactor the activity to use better Di, but a simple victory will be:

public class MyActivity extends ... {
   @VisibleForTest
   @RestrictTo(Scope.TESTS)
   protected StorageManager GetStorageManager() {
      ...
   }
}

@RunWith(RobolectricTestRunner.class)
@Config(constants = BuildConfig.class)
public class MyActivityTest {
    @Mock
    private StorageManager storageManagerMock;

    MyActivity myActivity;

    @Before
    public void setUp() {
        initMocks(this);
        ActivityController<TestMyActivity> activityController = Robolectric.buildActivity(TestMyActivity.class);
        myActivity = activityController.get();
       // when(registrationActivity.GetMetricManager()).thenReturn(mock(MetricsManager));
        activityController.setup();         
    }

...

   public class TestMyActivity extends MyActivity {
      protected StorageManager GetStorageManager() {
          return storageManagerMock;
      }
   }
}

This should be slightly modified