PowerMockito: Mocking Private and Public Static Methods

Assume following class with private and public static methods and we want to write junit test which access those methods. We are mocking these static methods.

	//=================================================================================================
	class MockStaticMethod {
	public int getResult(int a, int b, boolean sum) {
	if (sum) {
	return sum(a, b);
	} else {
	return diff(a, b);
	}
	} // getResult
	//-----------------------------------------------------------------------------------------------
	public static int sum(int a, int b) {
	return a + b;
	} // sum
	//-----------------------------------------------------------------------------------------------
	private static int diff(int a, int b) {
	return a - b;
	} // diff
	} // MockStaticMethod

view raw MockStaticMethodTest.java hosted with ❤ by GitHub

Mock Private Static Method

	@Test
	public void testDiff() throws Exception {
	PowerMockito.mockStatic(MockStaticMethod.class);
	PowerMockito.doReturn(3).when(MockStaticMethod.class, "diff", Mockito.anyInt(), Mockito.anyInt());
	MockStaticMethod obj = new MockStaticMethod();
	Assert.assertEquals(3, obj.getResult(0, 0, false));
	Assert.assertEquals(3, obj.getResult(1, 2, false));
	} // testDiff

view raw MockStaticMethodTest.java hosted with ❤ by GitHub

For mocking private static method we need to use

	PowerMockito.mockStatic(MockStaticMethod.class);
	PowerMockito.doReturn(3).when(MockStaticMethod.class, "diff", Mockito.anyInt(), Mockito.anyInt());

view raw MockStaticMethodTest.java hosted with ❤ by GitHub

Mock Public Static Method

When mocking public static method we could use either of following:

	PowerMockito.mockStatic(MockStaticMethod.class);
	PowerMockito.when(MockStaticMethod.sum(Mockito.anyInt(), Mockito.anyInt())).thenReturn(100);

view raw MockStaticMethodTest.java hosted with ❤ by GitHub

OR

	PowerMockito.mockStatic(MockStaticMethod.class);
	PowerMockito.doReturn(100).when(MockStaticMethod.class, "sum", Mockito.anyInt(), Mockito.anyInt());

view raw MockStaticMethodTest.java hosted with ❤ by GitHub

Here is the implementation

	@Test
	public void testSumRight() throws Exception {
	PowerMockito.mockStatic(MockStaticMethod.class);
	PowerMockito.when(MockStaticMethod.sum(Mockito.anyInt(), Mockito.anyInt())).thenReturn(100);
	MockStaticMethod obj = new MockStaticMethod();
	Assert.assertEquals(100, obj.getResult(0, 0, true));
	Assert.assertEquals(100, obj.getResult(1, 2, true));
	} // testSumRight
	//-----------------------------------------------------------------------------------------------
	@Test
	public void testSumRight2() throws Exception {
	PowerMockito.mockStatic(MockStaticMethod.class);
	PowerMockito.doReturn(100).when(MockStaticMethod.class, "sum", Mockito.anyInt(), Mockito.anyInt());
	MockStaticMethod obj = new MockStaticMethod();
	Assert.assertEquals(100, obj.getResult(0, 0, true));
	Assert.assertEquals(100, obj.getResult(1, 2, true));
	} // testSumRight2

view raw MockStaticMethodTest.java hosted with ❤ by GitHub

BE CAREFUL NOT USE FOLLOWING WITH PUBLIC STATIC METHOD

	@Test
	public void testSumWrong() throws Exception {
	PowerMockito.mockStatic(MockStaticMethod.class);
	PowerMockito.doReturn(100).when(MockStaticMethod.sum(Mockito.anyInt(), Mockito.anyInt()));
	MockStaticMethod obj = new MockStaticMethod();
	Assert.assertEquals(100, obj.getResult(0, 0, true));
	Assert.assertEquals(100, obj.getResult(1, 2, true));
	} // testSumWrong

view raw MockStaticMethodTest.java hosted with ❤ by GitHub

This will give ERROR

  org.mockito.exceptions.misusing.UnfinishedStubbingException: 
  Unfinished stubbing detected here:
  -> at org.powermock.api.mockito.internal.PowerMockitoCore.doAnswer(PowerMockitoCore.java:36)

  E.g. thenReturn() may be missing.
  Examples of correct stubbing:
      when(mock.isOk()).thenReturn(true);
      when(mock.isOk()).thenThrow(exception);
      doThrow(exception).when(mock).someVoidMethod();
  Hints:
   1. missing thenReturn()
   2. you are trying to stub a final method, you naughty developer!
   3: you are stubbing the behaviour of another mock inside before 'thenReturn' instruction if completed      
      

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