What is the difference between mocking and spying in Jest?

What is the difference between mocking and spying in Jest?

In Jest, mocking creates a fake version of a function, while spying allows you to track calls to a function without replacing it.

Can you give me an example of when to use mocking?

Sure! Use mocking when you want to isolate a unit test from external dependencies, like API calls.

And when should I use spying instead?

Spying is useful when you want to verify that a function was called with specific arguments without altering its behavior.

Are there any performance implications of using mocks or spies?

Yes, mocks can be faster since they don't execute the actual implementation, but excessive mocking can lead to less reliable tests.