Can I use async/await in Jest, when the tested function is not using async/await?

I have a simple controller for adding new users. After the successful resolution (user added), the controller sends a 202 response. As you can see, the function is promise based and is not using async/await.

const addUserController = function (req, res, next) {
    Users.addOne(req.userid, req.body.email)
    .then(() => {
      res.status(202).send();
    })
    .catch((err) => {
      console.log(err);
      res.status(500).json({ message: "Internal server error." });
    });
};

When I am testing this function in Jest with the, the function executes immediately, without going to the then() part, resulting in a mistaken 200 code, instead of 202, so the following test fails:

it("Should add a user", () => {
    let req, res, next, pool;
    pool = new Pool();
    req = httpsMocks.createRequest();
    res = httpsMocks.createResponse();
    res.next = null;
    req.userid = 1;
    req.body = {
      id: 2
    }
    pool.query.mockResolvedValue({rows:[], rowCount: 1});
    apiController.addUserController(req, res, next);
    expect(res.statusCode).toBe(202);
    expect(pool.query).toBeCalledTimes(1);
});

However, when I make it like that:

it("Should add a user", async () => {
    let req, res, next, pool;
    pool = new Pool();
    req = httpsMocks.createRequest();
    res = httpsMocks.createResponse();
    res.next = null;
    req.userid = 1;
    req.body = {
      id: 2
    }
    pool.query.mockResolvedValue({rows:[], rowCount: 1});
    await apiController.addUserController(req, res, next);
    expect(res.statusCode).toBe(202);
    expect(pool.query).toBeCalledTimes(1);
});

that is I add async/await, it works alright – the response status code is 202, meaning the function was awaited and the test passes.
But why? When I hover over the newly added ‘await’ VS code is suggesting that

‘await’ has no effect on the type of this expression.

Well it makes sense – it should have no effect, as the tested function is not async, so it shouldn’t work, but well, it works – only when I add the async/await to the Jest function it works fine.

Could someone explain this to me?