Test helper utility to expect a function or a promise to throw

usage.ts

// usage examples

// callback
const err1 = await waitError(() => { /* do something that throws */ })

// async callback
const err2 = await waitError(async () => { /* do something async that throws */ })

// expect a promise instance to throw
const err3 = await waitError(promise) 



// expect a promise instance to throw with a specific error constructor
const err4 = await waitError(promise, MyCustomError)

waitError.ts

type Constructor<T extends {} = {}> = new (...args: any[]) => T;

export async function waitError<TError = Error>(
  /**
   * Function callback or promise that you expect will throw
   */
  fnOrPromise: (() => Promise<unknown> | unknown) | Promise<unknown>,
  /**
   * Force error constructor to be of specific type
   * @default Error
   **/
  errorConstructor?: Constructor<TError>,
): Promise<TError> {
  try {
    if (typeof fnOrPromise === 'function') {
      await fnOrPromise();
    } else {
      await fnOrPromise;
    }
  } catch (err) {
    expect(err).toBeInstanceOf(errorConstructor ?? Error);
    return err as TError;
  }
  throw new Error('Function did not throw');
}