Learning Redux

Exceptions

It is not enough to test successful cases; sometimes you also need to test certain failing cases (for example, invalid username handled properly).

When you want to test if a function throws an error when it is called, you can use the toThrow matcher; for example:

function failingTest () {  throw new Error('this is supposed to fail!')}test('failing test', () => {  expect(failingTest).toThrow()})

You can also match on the error type, which is useful if you have defined custom errors. For example, to only match an APIError:

expect(failingTest).toThrow(APIError)

Or, you can match on the error message; for example:

expect(failingTest).toThrow(/supposed to fail/)