What are the best practices for unit testing and mock testing in Python applications?

In simple terms, unit tests are like precision tools to ensure every component works as expected. You should use `unittest` or `pytest` for writing your tests, and focus on testing one piece of functionality per test for clarity. When it comes to mock testing, use `unittest.mock` to simulate external dependencies or behaviors. This is like creating a controlled environment to test how your code interacts with external systems without the overhead of actual system calls. Remember, tests are not just for finding errors; they're your safeguard against future changes breaking your carefully crafted machine.