mocha test get timeout when await a new Promise which's executor is async and throw error inside

Question

I'm using mocha for testing, when I code below, the test will get timeout:

describe("myTest", () => {
  it("myTest-0", async () => {
    await new Promise(async (res, rej) => {
      throw new Error("this is error");
    });
  });
});

=========================================================

but if I remove new Promise executor's async prefix, the test will throw error immediately:

describe("myTest", () => {
  it("myTest-0", () => {
    await new Promise(async (res, rej) => {
      throw new Error("this is error");
    });
  });
});

=========================================

why the first one get timeout instead of throwing error immediately?