AssertionError [ERR_ASSERTION]: Missing expected rejection (Error)

Question

So, I am trying to write some unit tests for my code using MochaJS, SinonJS, rewire, chai and assert. An i got the following error:

 1) async function addOneRoom(db, newRoom)
   should reject error when the maximum room number has been reached:
 AssertionError [ERR_ASSERTION]: Missing expected rejection (Error).
  at async Context.<anonymous> (test\test.js:33:9).

So the function I am testing is the following one:

async function addOneRoom(db, newRoom) {
const roomNumber = await createRoomNumber(db, newRoom.floor);

if (roomNumber !== 0) {
    newRoom.roomNumber = roomNumber;
    const result = await db.rooms.insertOne(newRoom);
    return newRoom
} else return new Error("No room can be added on this floor. The maximum numar of rooms has been reached")}

And my unit test for it is:

describe("async function addOneRoom(db, newRoom)", () => {
const addOneRoom = rewired.__get__("addOneRoom")
const sandBox = sinon.createSandbox()

it("should reject error when the maximum room number has been reached", async () => {
    const newRoom = {
        floor: 1,
        sqm: 20,
        capacity: 5,
        features: {
            videoProjector: 1,
            stage: 2
        }
    }

    const insertOne = sandBox.stub().returns()
    const mockedCreateRoomNumber = sandBox.stub().resolves(0)

    const db = {
        rooms: { insertOne }
    }

    const stubbedRoomNumber = rewired.__set__({ createRoomNumber: mockedCreateRoomNumber })
    await assert.rejects(addOneRoom(db, newRoom), new Error("No room can be added on this floor. The maximum numar of rooms has been reached"))

    // sandBox.assert.calledOnceWithExactly(stubbedRoomNumber)
    sandBox.assert.calledOnceWithExactly(insertOne, {newRoom})

    const order = [
        // stubbedRoomNumber,
        insertOne
    ]

    sandBox.assert.callOrder(...order)
    stubbedRoomNumber()
})

I would appreciate any help!

Answer 1

Don't return the Error, throw it:

throw new Error("No room can be added on this floor. The maximum numar of rooms has been reached")}

Returning an Error is no different from returning anything else, and will not cause a promise rejection.