Mock a new route, or override an existing handler.

The route uses path-to-regexp syntax, with the additional extension of (optional) method routing (prefix with METHOD@, eg. POST@/user/:id).

The handler function can either be a function or an async function.

mock("GET@/users/:id", async (_req, match) => {
  const id = parseInt(match.params["id"]);
  const data = await magicallyGetMyUserData(id);
  return new Response(JSON.stringify(data));
})