Updating existing tests to use the matcher

In this final section, we’ll use the matcher we’ve just built to simplify the form validation error test suite.

Let’s get started:

1. First, register the matcher for our test runs by adding an import statement and call to expect.extend in the src/vitest/registerMatchers.js file:

   ...
   import {
     toBeUnprocessableEntity
   } from './src/matchers/toBeUnprocessableEntity.js';
   ...
   expect.extend({ toBeUnprocessableEntity });

2. Then, in src/routes/birthdays/page.server.test.js, find the nested describe block with the description when the name is not provided. It contains four tests. Leave the first one in place, and replace the last three tests with the following test:

   describe('when the name is not provided', () => {
     ...
     it('does not save the birthday', ...);
     it('returns a complete error response', () => {
       ...