I have a function like this:
export const myFunc = (a, b ,callBack) => {
const timer = setTimeout(() => {
callBack(a+b);
}, 10);
return () => clearTimeout(timer);
};
I'm able to test the callback function just fine by doing this:
jest.useFakeTimers();
describe('myFunc', () => {
const callBack = jest.fn();
it('runs myFunc', () => {
myFunc(1, 2, callBack);
jest.runAllTimers();
expect(callBack).toHaveBeenCalledWith(3);
});
However, the last line return () => clearTimeout(timer) is never tested somehow. Jest report just says this line function not covered and statement not covered. Can anyone please tell me a way to cover this line without using any other external testing library like enzyme?
The function isn't called, so it's not covered.
Another test would be:
let cleanup = myFunc(1, 2, callBack);
cleanup()
jest.runAllTimers();
expect(callBack).not.toHaveBeenCalled();