Shared Preferences is null in mockito

Issue

I am trying to mock a simple shared preferences using Mockito . Since, the examples on google are too complicated to make anything out of it, I decided to go ahead on my own. The shared preferences are setup using dagger. It crashes with NPE in the saveString method in the SharedPreferenceManager class on the putString line.

@Module
public class StudentModule {
    @Provides
    @Singleton
    static Context getContext(Application application) {
        return application.getApplicationContext();
    }

    @Provides
    @Singleton
    static SharedPreferences getSharedPreferences(Context context) {
        return PreferenceManager.getDefaultSharedPreferences(context);
    }
}

There is a manager class:

public class SharedPreferenceManager {
    private SharedPreferences sharedPreferences;
    private Context context;
    @Inject public SharedPreferenceManager(SharedPreferences sharedPreferences, Context context){
        this.sharedPreferences=sharedPreferences;
        this.context=context;
    }
    public String doSomething(){

        return sharedPreferences.getString("s","");
    }
    public void saveString(String s){
        System.out.println(sharedPreferences.getClass().getSimpleName());
        SharedPreferences.Editor editor=sharedPreferences.edit();
        editor.putString("s","bis").apply();

    }
}

Here is the test:

@RunWith(MockitoJUnitRunner.class)

public class MockTest {
    @InjectMocks
    SharedPreferenceManager sharedPreferenceManager;
    @Mock SharedPreferences sharedPreferences;


    @Before
    public void setup() {
        MockitoAnnotations.initMocks(this);



    }
    @Test
    public void isSharedPefWorking(){
        sharedPreferenceManager.saveString("bis");
        assertEquals("bis",sharedPreferenceManager.doSomething());

    }

}

Solution

SharedPreferences uses a SharedPreferences.Editor which you're not currently mocking.

You would need to do something like the following to mock and verify the behaviour of your SharedPreferenceManager.

@RunWith(MockitoJUnitRunner.class)
public class MockTest {
    @InjectMocks
    SharedPreferenceManager sharedPreferenceManager;
    @Mock
    SharedPreferences sharedPreferences;
    @Mock
    SharedPreferences.Editor sharedPreferencesEditor;

    final String savedString = "savedString";

    @Before
    public void setup() {
        MockitoAnnotations.initMocks(this);
        when(sharedPreferences.edit()).thenReturn(sharedPreferencesEditor);
        when(sharedPreferencesEditor.putString(anyString(), anyString())).thenReturn(sharedPreferencesEditor);
    }

    @Test
    public void saveString() {
        sharedPreferenceManager.saveString(savedString);
        verify(sharedPreferencesEditor).putString("s", savedString);
    }

    @Test
    public void getString() {
        when(sharedPreferences.getString("s","")).thenReturn(savedString);

        String preferenceString = sharedPreferenceManager.doSomething();

        assertEquals(preferenceString, savedString);
    }

}

Answered By - Chris