relative pathname in Request not working on POST request

test("GET: all car brands", async () => {
  const res = await app.request("/api/brand");
  const body = await res.json();
  // [{ id: 0, name: "BMW" }, { id: 1, name: "Audi" }]
});

test("POST: create new car brand", async () => {
  ...
  ...
  const req = new Request("/api/brand", {
    method: "POST",
    body: formData,
  });
  
  await app.request(req);
  ...
  ...

  /*
    41 |     const req = new Request("/api/brand", {
                       ^
    TypeError: Failed to construct 'Request': Invalid URL "/api/brand"
     code: "ERR_INVALID_URL"
  */
});