What is the difference between spies and mocks in testing?

What is the difference between spies and mocks in testing?

In testing, a mock is a simulated object that mimics the behavior of real objects, while a spy records information about how it was called.

Can you give me an example of when to use a spy?

Sure! Use a spy when you want to verify that a function was called with specific arguments without altering its behavior.

And when should I use a mock instead?

Use a mock when you want to simulate the behavior of a dependency and control its responses during testing.

Are there any libraries you recommend for using mocks and spies?

Yes! Popular libraries include Jest for JavaScript, Mockito for Java, and unittest.mock for Python.