Android – Mocking method calls using power mockito – org.powermock.api.mockito.ClassNotPreparedException

androidjunitmockitopowermockunit testing

I have an image loader class and i need to test some static methods in it. Since Mockito does not support static methods i switched to Power Mockito. But the static method i am testing has a method call

 Base64.encodeToString(byteArray, Base64.DEFAULT);

To mock this i am using mockStatic method as below with @PrepareForTest annotation.

 PowerMockito.mockStatic(Base64.class);

But Android studio is returning me still returning me an error as below.

org.powermock.api.mockito.ClassNotPreparedException: The class
android.util.Base64 not prepared for test. To prepare this class, add
class to the '@PrepareForTest' annotation.

Below is my complete code.

Code to be tested:

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.util.Base64;
import android.widget.ImageView;

  public static String convertBitmapToBase64(Bitmap imageBitmap, boolean withCompression) {
    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
    imageBitmap.compress(Bitmap.CompressFormat.PNG, 120, byteArrayOutputStream);
    byte[] byteArray = byteArrayOutputStream.toByteArray();
    return Base64.encodeToString(byteArray, Base64.DEFAULT);
}

Test class code

import android.graphics.Bitmap;
import android.util.Base64;
import org.junit.Before;
import org.junit.runner.RunWith;
import org.mockito.MockitoAnnotations;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;
import org.testng.annotations.Test;

@RunWith(PowerMockRunner.class)
@PrepareForTest({Base64.class})
public class ImageLoaderTest  {
@Test
   public void testConvertBitmap(){
    byte[] array = new byte[20];
    PowerMockito.mockStatic(Base64.class);
    PowerMockito.when(Base64.encodeToString(array, Base64.DEFAULT)).thenReturn("asdfghjkl");
    Bitmap mockedBitmap= PowerMockito.mock(Bitmap.class);
    String output = ImageLoaderUtils.convertBitmapToBase64(mockedBitmap);
    assert (!output.isEmpty());
}

}

Gradle dependencies

testCompile 'junit:junit:4.12'
testCompile 'org.powermock:powermock:1.6.5'
testCompile 'org.powermock:powermock-module-junit4:1.6.5'
testCompile 'org.powermock:powermock-api-mockito:1.6.5'

Best Answer

Short answer you can't. Here from the FAQ:

What are the limitations of Mockito

Cannot mock final classes

Cannot mock static methods

Cannot mock final methods - their real behavior is executed without any exception. Mockito cannot warn you about mocking final methods so be vigilant.

Further information about this limitation:

Can I mock static methods?

No. Mockito prefers object orientation and dependency injection over static, procedural code that is hard to understand & change. If you deal with scary legacy code you can use JMockit or Powermock to mock static methods.

If you want to use PowerMock try like this:

@RunWith(PowerMockRunner.class)
@PrepareForTest( { Base64.class })
public class YourTestCase {
    @Test
    public void testStatic() {
        mockStatic(Base64.class);
        when(Base64.encodeToString(argument)).thenReturn("expected result");
    }
}

EDIT: In Mockito 2 it's now possible to mock final Class and final Method. It's an opt-in option. You need to create the file src/test/resources/mockito-extensions/org.mockito.plugins.MockMaker with the following content:

mock-maker-inline

EDIT 2: Since Mockito 3.4.0 its now possible to mock static method too:

try (MockedStatic mocked = mockStatic(Base64.class)) {
    mocked.when(() -> Base64.encodeToString(eq(array), eq(Base64.DEFAULT))).thenReturn("bar");
    assertEquals("bar", Base64.encodeToString(array, Base64.DEFAULT));
    mocked.verify(() -> Base64.encodeToString(any(), anyIn());
}

Furthermore you can directly add as a dependency org.mockito:mockito-inline:+ and avoid manually create the or.mockito.plugins.MockMaker file

Since Mockito 3.5.0 you can also mock object construction.

Related Solutions

Android – How to save an activity state using the save instance state

You need to override onSaveInstanceState(Bundle savedInstanceState) and write the application state values you want to change to the Bundle parameter like this:

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
  super.onSaveInstanceState(savedInstanceState);
  // Save UI state changes to the savedInstanceState.
  // This bundle will be passed to onCreate if the process is
  // killed and restarted.
  savedInstanceState.putBoolean("MyBoolean", true);
  savedInstanceState.putDouble("myDouble", 1.9);
  savedInstanceState.putInt("MyInt", 1);
  savedInstanceState.putString("MyString", "Welcome back to Android");
  // etc.
}

The Bundle is essentially a way of storing a NVP ("Name-Value Pair") map, and it will get passed in to onCreate() and also onRestoreInstanceState() where you would then extract the values from activity like this:

@Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
  super.onRestoreInstanceState(savedInstanceState);
  // Restore UI state from the savedInstanceState.
  // This bundle has also been passed to onCreate.
  boolean myBoolean = savedInstanceState.getBoolean("MyBoolean");
  double myDouble = savedInstanceState.getDouble("myDouble");
  int myInt = savedInstanceState.getInt("MyInt");
  String myString = savedInstanceState.getString("MyString");
}

Or from a fragment.

@Override
public void onViewStateRestored(@Nullable Bundle savedInstanceState) {
    super.onViewStateRestored(savedInstanceState);
    // Restore UI state from the savedInstanceState.
    // This bundle has also been passed to onCreate.
    boolean myBoolean = savedInstanceState.getBoolean("MyBoolean");
    double myDouble = savedInstanceState.getDouble("myDouble");
    int myInt = savedInstanceState.getInt("MyInt");
    String myString = savedInstanceState.getString("MyString");
}

You would usually use this technique to store instance values for your application (selections, unsaved text, etc.).

Java – How to mock void methods with Mockito

Take a look at the Mockito API docs. As the linked document mentions (Point # 12) you can use any of the doThrow(),doAnswer(),doNothing(),doReturn() family of methods from Mockito framework to mock void methods.

For example,

Mockito.doThrow(new Exception()).when(instance).methodName();

or if you want to combine it with follow-up behavior,

Mockito.doThrow(new Exception()).doNothing().when(instance).methodName();

Presuming that you are looking at mocking the setter setState(String s) in the class World below is the code uses doAnswer method to mock the setState.

World mockWorld = mock(World.class); 
doAnswer(new Answer<Void>() {
    public Void answer(InvocationOnMock invocation) {
      Object[] args = invocation.getArguments();
      System.out.println("called with arguments: " + Arrays.toString(args));
      return null;
    }
}).when(mockWorld).setState(anyString());

Best Answer

Related Solutions

Android – How to save an activity state using the save instance state

Java – How to mock void methods with Mockito

Related Topic