[Solved] Mocking method calls using power mockito – org.powermock.api.mockito.ClassNotPreparedException

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.


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.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.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;

public class ImageLoaderTest  {
   public void testConvertBitmap(){
    byte[] array = new byte[20];
    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'

Solution #1:

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:

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

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:


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.

Respondent: Ajith Memana

The answers/resolutions are collected from stackoverflow, are licensed under cc by-sa 2.5 , cc by-sa 3.0 and cc by-sa 4.0 .

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