Checking for null or not

There is a school of thought that checking for null in tests is redundant and can be removed all together. In other words, the second-to-last test we wrote would become this:

it('renders a label for the first name field', () => {
  render();
  expect(labelFor('firstName').textContent).toEqual('First name');
});

In the original test, the first not null expectation is a guard expectation. The test will still function even without this line, since the second expectation will throw an exception if the value of label is null.

The run-time difference between the two variants of the test is subtle. The original test will fail with a test failure, not an exception. In this second version, your test will fail with an exception, not a test failure.

In some languages and test environments, exceptions can be more painful than test failures. Ultimately, which style you choose is a matter of personal preference. In this book, I'll continue to use guard expectations for completeness, but I'd encourage you to experiment with both styles.