Yes, mocking private methods can potentially lead to brittle tests. There are a few reasons why this can be the case:
1. Tight Coupling to Implementation Details: When you mock a private method, you are tightly coupling your test to the internal implementation of the class under test. This means that if the implementation of the private method changes, your test will likely break, even if the public API of the class remains the same.
2. Fragile Tests: Private methods are often implementation details that can change frequently during development. By mocking these private methods, you are making your tests more fragile and susceptible to breaking when the implementation changes.
3. Lack of Abstraction: Mocking private methods can indicate that your class has too many responsibilities or is not sufficiently abstracted. It may be a sign that the class should be refactored to have a more focused, single responsibility.
4. Maintenance Overhead: Maintaining tests that mock private methods can be more time-consuming, as you need to update the mocks whenever the private method implementation changes.
Instead of mocking private methods, it's generally recommended to focus on testing the public API of your classes. This helps ensure that your tests are more robust and less dependent on implementation details. If you find that you need to test the behavior of a private method, consider refactoring your code to make that behavior more accessible through the public API.
Some alternative approaches to mocking private methods include:
1. Use Spies: Mockito's `spy()` method allows you to create a partial mock of an object, which can be used to override the behavior of private methods.
2. Extract to a Separate Class: If a private method has significant logic, consider extracting it to a separate class or module, which can then be tested independently.
3. Use Reflection: In some cases, you may be able to use reflection to access and test private methods, but this approach should be used sparingly as it can also lead to fragile tests.
By following these best practices, you can write more maintainable and robust tests that are less dependent on the internal implementation details of your classes.
Citations:[1] https://intellipaat.com/blog/tutorial/mockito-tutorial/methods-of-mockito/
[2] https://ioflood.com/blog/mockito-verify/
[3] https://www.toptal.com/java/a-guide-to-everyday-mockito
[4] https://www.vogella.com/tutorials/Mockito/article.html
[5] https://semaphoreci.com/community/tutorials/stubbing-and-mocking-with-mockito-2-and-junit