What does @PrepareForTest in PowerMock really mean?

Question

What does the annotation @PrepareForTest in PowerMockito really mean?

What should be placed there apart of classes which have static methods?

Answer 1

That annotation tells PowerMock(ito) that the listed classes will need to be manipulated on the byte code level.

You need to "prepare for test" all these classes X of which you want to

• mock a static method (on X)
• gain control over calls to new() used in another class X
• gain control over private methods (which you do using a spy and
  PowerMockito.when(spy, "privateMethodNameAsString").then...

In other words:

• To mock X.doStatic(), you have to prepare the class X.
• To control new Y(...), you have to prepare the class X that contains that new statement.