What are the differences between mocks and spies in testing?

What are the differences between mocks and spies in testing?

Mocks and spies are both used in testing to isolate components, but they serve different purposes. Mocks are used to simulate the behavior of complex objects, while spies allow you to track how a function is called without altering its behavior.

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

Sure! You would use a mock when you want to test a function that depends on an external service, like an API call, without actually hitting the API.

And what about spies? When should I use them?

Spies are useful when you want to verify that a function was called with specific arguments or how many times it was called, without changing its implementation.

Are there any libraries that help with mocks and spies?

Yes, popular testing libraries like Jest and Sinon provide built-in support for creating mocks and spies, making it easier to implement them in your tests.