Combining Real Object Behavior with Mocked Behavior

When it comes to writing unit tests for your Java application, using mock objects can greatly simplify the process. Mock objects allow you to replace dependencies of the class under test with test-specific implementations, enabling you to isolate and focus on the behavior of the class itself.

One popular mocking framework for Java is Mockito. Mockito provides a simple and intuitive API for creating and working with mock objects. However, there may be scenarios where you need to combine the real behavior of an object with mocked behavior. This can be useful when testing complex or partially implemented classes.

Thankfully, Mockito provides a way to combine real object behavior with mocked behavior. This can be achieved using the CALLS_REAL_METHODS option when creating the mock.

Consider a scenario where you have a class Calculator with a method add that performs addition of two numbers. Let's assume that the add method calls a private helper method validateInput to ensure that the input numbers are valid. In this case, you may want to mock the validation behavior and verify that the add method is called, while still allowing the real addition operation to be performed.

Here's how you can combine both behaviors using Mockito:

// Create a mock object with real behavior
Calculator calculatorMock = Mockito.mock(Calculator.class, Mockito.CALLS_REAL_METHODS);

// Mock the validation behavior
Mockito.doNothing().when(calculatorMock).validateInput(Mockito.anyInt(), Mockito.anyInt());

// Perform the real addition operation
int result = calculatorMock.add(2, 3);

// Verify that the add method was called
Mockito.verify(calculatorMock).add(Mockito.anyInt(), Mockito.anyInt());

// Assert the result
assertEquals(5, result);

In the above example, we create a mock object of the Calculator class and specify the CALLS_REAL_METHODS option to allow the real behavior. Then, we mock the validateInput method using doNothing to bypass its execution. Finally, we can call the add method on the mock object, which will perform the real addition operation while still allowing us to verify its invocation.

It's important to note that when combining real object behavior with mocked behavior, only the specified methods will exhibit the real behavior. All other methods will be mocked as usual.

In conclusion, Mockito provides a powerful feature to combine real object behavior with mocked behavior. This can be especially useful when testing complex classes that require partial mocking. By using the CALLS_REAL_METHODS option and mocking specific behavior, you can effectively test and verify the desired functionality while maintaining control over dependencies.

So, next time you come across a scenario where you need to combine real and mocked behavior, rest assured that Mockito has got you covered!