How to mock a SharedPreferences using Mockito

Question

I have just read about Unit Instrumented Testing in Android and I wonder how I can mock a SharedPreferences without any SharedPreferencesHelper class on it like here

My code is:

public class Auth {
private static SharedPreferences loggedUserData = null;
public static String getValidToken(Context context)
{
    initLoggedUserPreferences(context);
    String token = loggedUserData.getString(Constants.USER_TOKEN,null);
    return token;
}
public static String getLoggedUser(Context context)
{
    initLoggedUserPreferences(context);
    String user = loggedUserData.getString(Constants.LOGGED_USERNAME,null);
    return user;
}
public static void setUserCredentials(Context context, String username, String token)
{
    initLoggedUserPreferences(context);
    loggedUserData.edit().putString(Constants.LOGGED_USERNAME, username).commit();
    loggedUserData.edit().putString(Constants.USER_TOKEN,token).commit();
}

public static HashMap<String, String> setHeaders(String username, String password)
{
    HashMap<String, String> headers = new HashMap<String, String>();
    String auth = username + ":" + password;
    String encoding = Base64.encodeToString(auth.getBytes(), Base64.DEFAULT);
    headers.put("Authorization", "Basic " + encoding);
    return headers;
}

public static void deleteToken(Context context)
{
    initLoggedUserPreferences(context);
    loggedUserData.edit().remove(Constants.LOGGED_USERNAME).commit();
    loggedUserData.edit().remove(Constants.USER_TOKEN).commit();
}

public static HashMap<String, String> setHeadersWithToken(String token) {
    HashMap<String, String> headers = new HashMap<String, String>();
    headers.put("Authorization","Token "+token);
    return headers;
}
private static SharedPreferences initLoggedUserPreferences(Context context)
{
    if(loggedUserData == null)
        loggedUserData = context.getSharedPreferences(Constants.LOGGED_USER_PREFERENCES,0);
    return loggedUserData;
}}

Is is possible to mock SharedPreferences without creating other class on it?

Answer 1

So, because SharedPreferences comes from your context, it's easy:

final SharedPreferences sharedPrefs = Mockito.mock(SharedPreferences.class);
final Context context = Mockito.mock(Context.class);
Mockito.when(context.getSharedPreferences(anyString(), anyInt())).thenReturn(sharedPrefs);

// no use context

for example, for getValidToken(Context context), the test could be:

@Before
public void before() throws Exception {
    this.sharedPrefs = Mockito.mock(SharedPreferences.class);
    this.context = Mockito.mock(Context.class);
    Mockito.when(context.getSharedPreferences(anyString(), anyInt())).thenReturn(sharedPrefs);
}

@Test
public void testGetValidToken() throws Exception {
    Mockito.when(sharedPrefs.getString(anyString(), anyString())).thenReturn("foobar");
    assertEquals("foobar", Auth.getValidToken(context));
    // maybe add some verify();
}

Answer 2

The following example shows how you might create a unit test that uses a mock Context object such as shared preference.

@RunWith(MockitoJUnitRunner.class)
public class MProfileTest {

   @Mock
   Context mockContext;
   @Mock
   SharedPreferences mockPrefs;
   @Mock
   SharedPreferences.Editor mockEditor;

   @Before
   public void before() throws Exception {

      Mockito.when(mockContext.getSharedPreferences(anyString(), anyInt())).thenReturn(mockPrefs);
      Mockito.when(mockContext.getSharedPreferences(anyString(), anyInt()).edit()).thenReturn(mockEditor);

      Mockito.when(mockPrefs.getString("YOUR_KEY", null)).thenReturn("YOUR_VALUE");
   }

   @Test
   public void anyTest() {
      // Any shared preference you can call
      // Assert.assertTrue();
      String val = _mockPrefs.getString("YOUR_KEY", null); // It returns YOUR_VALUE
   }
}

If you face any issues on importing mock framework just make sure you have added the depencencies in your app/build.gradle file.

https://developer.android.com/training/testing/unit-testing/local-unit-tests#setup

---

If you want to use real shared prefrence as your device by storing all the data in memory, follow the below code.

Get the MockSharedPreference.java file from this Gist https://gist.github.com/aslamanver/f74a2b3d450fda251d47a0d38b44edb7

@Mock
Context mockContext;

MockSharedPreference mockPrefs;
MockSharedPreference.Editor mockPrefsEditor;

@Before
public void before() {

    mockPrefs = new MockSharedPreference();
    mockPrefsEditor = mockPrefs.edit();

    Mockito.when(mockContext.getSharedPreferences(anyString(), anyInt())).thenReturn(mockPrefs);
}

Answer 3

There is a better way to mock SharedPreferences, IMHO. I like Mockito, but it is unproductive to mock SharedPreferences in every test.

Luckily, we can use the shared-preferences-mock library. This library implements SharedPrefences on JVM, so it behaves like a real class. Moreover, it is possible to write local unit tests.

For your case:

import com.github.ivanshafran.sharedpreferencesmock.SPMockBuilder;

class Test {
    private Context context;
    private SharedPreferences sharedPreferences;

    @Before
    public void setUp() {
        this.sharedPreferences = new SPMockBuilder().createSharedPreferences();
        this.context = Mockito.mock(Context.class);         
        Mockito.when(context.getSharedPreferences(Constants.LOGGED_USER_PREFERENCES,0))
            .thenReturn(sharedPreferences);
    }

    @Test
    public void test() {
        sharedPreferences.edit().putString(Constants.LOGGED_USERNAME, "admin").commit();
        String value = Auth.getLoggedUser(context);
        asssertEquals("admin", value);
    }

}

Add it to your root build.gradle at the end of repositories:

allprojects {
    repositories {
        maven { url 'https://jitpack.io' }
    }
}

Add the dependency:

dependencies {
    testImplementation 'com.github.IvanShafran:shared-preferences-mock:1.0'
}