How to Mock Specific Static Methods Returning Objects in Java Using Mockito and PowerMock?

Mocking Specific Static Methods to Return Objects

Mockito and PowerMock provide robust support for mocking static methods. However, it can be tricky to mock a single static method and have it return an object.

Avoid Mismatch and Call Issue

When mocking a static method that returns an object, it's important to avoid mismatches in return types. Mocking all static methods with a default strategy (such as returning null for object-valued methods) can lead to errors.

PowerMockito.mockStatic(Static.class, new Answer()) will mock all methods, including m2, which has a different return type. Similarly, PowerMockito.when(Static.m1(param1, param2)).thenReturn(1000l) will not be called because the static method has not been mocked properly.

Enable Static Mocking and Target Specific Method

The solution is to combine the concepts of static method mocking and targeted method stubbing. PowerMockito.mockStatic enables static mocking for a class, while when-thenReturn syntax allows you to stub specific methods.

PowerMockito.mockStatic(Static.class);
when(Static.m1(param1, param2)).thenReturn(1000l);

This approach enables static mocking for all methods of Static.class but does not override the default stubbing strategy. By using when-thenReturn, you explicitly stub the m1 method to return 1000l.

Consider the MockStatic Overloads

PowerMockito provides two overloads for mockStatic. The one-argument overload (mockStatic(Static.class)) enables static mocking without a default strategy. The two-argument overload (mockStatic(Static.class, Answer())) allows you to provide a default strategy for mocked methods.

Depending on your specific testing scenario, you may choose to use either of these overloads. If you want to mock only a specific method or set multiple return values for different method calls, the one-argument overload is more appropriate.

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