Reasons to use getBy* in conjunction with toBeInTheDocument

Question

There are plenty of examples of getBy* or findBy* queries are used in conjunction with expect().toBeInTheDocument() . At the same timethe Testing Library docs say that both of those type of queries throw errors when 0 elements match.

So there is a situation that when we do expect(screen.getByText('some text')).toBeInTheDocument() we're checking the element presence twice, which is redundant.

What's the reason everyone's doing this?

Answer 1

It's purely for readability. You don't really need the assertion .toBeInTheDocument() , or any other. As you say, in the failing case the error that fails the test is actually thrown by the getBy* method - expect is never even called.

However, using the expect(actual).matcher(expected) form makes it clearer that you're asserting on the presence of the element, whereas having getBy* on its own isn't very explicit. Readers will expect a test to have a certain "ryhthm", where some preconditions are set up (Arrange or Given), some action is taken (Act or When), and some postconditions are checked (Assert or Then). If a test ends without any expect ations, that can look like a mistake.

You may also have lint rules (like jest/expect-expect , although that can be configured to include getBy* as expectations) or Jest's own expect.hasAssertions() that will be unhappy if you leave the assertion to be implicit, even in the passing case. Testing Library has its own ESLint rules, which includes testing-library/prefer-explicit-assert covering this behaviour too.