mockPool
  .intercept({
    path: '/test',
    method: 'GET',
  })
  .reply(200, ({ headers }) => ({
    myHeader: headers.get('foo'),
  }));


const res = await fetch('http://localhost:3000/test', {
    headers: {
      foo: 'bar',
    },
  }).then((res) => res.json());

console.log(res); // Prints { myHeader: 'bar' }