Extracting test helpers

The Git tag for this section is extracting-test-helpers.

It's time to dry up our code. We'll do this in two ways:

• Replace our stub and spy with Jest's built-in spy functionality
• Extract repeated test code into their own files that can be reused across test suites

Using Jest to spy and stub

So far in this chapter you've built a usable set of spy and stub functions. Jest has built-in functionality that does the same thing but works slightly differently.

Here's a rundown of Jest test double support and how it compares to what you've built. We'll convert our CustomerForm tests to use these new functions in just a moment:

• To create a new spy, call jest.fn(). For example...