Test a custom validator with Jest Spectator

Question

I try to run a test that checks the proper functioning of a date validator. This validator returns an error if the first date entered is greater than the second. Everything works well at the code level. For some reason I do not know the following test does not work. Here is the validator in question:

export function compareTwoDatesValidator(
  dateFrom: string,
  dateTo: string
): ValidatorFn {
  return (form: AbstractControl): ValidationErrors | null => {
    let dateFromForm: string = form.get(dateFrom)?.value;
    let dateToForm: string = form.get(dateTo)?.value;
    const regEx = /^[12]\d{3}-\d{2}-\d{2}$/;

    if (!dateFromForm || !dateToForm) {
      return null;
    }

    if (dateFromForm.match(regEx) && dateToForm.match(regEx)) {
      let dateTime = luxon.DateTime;
      let dateDebut = dateTime.fromISO(dateFromForm);
      let dateFin = dateTime.fromISO(dateToForm);

      if (dateDebut.startOf('day') > dateFin.startOf('day')) {
        return {
          incorrectRangeDate: {
            dateFrom: dateFromForm,
            dateTo: dateToForm
          }
        };
      }
    }
    return null;
  };
}

In the unit test, I create a fake form that takes 2 FormControl with dates in string format I assign a value higher than the first date and I expect my form to contain an error but it does not. Here's my test:

describe('compareTwoDatesValidator', () => {
  let dateDebut: AbstractControl | null;
  let dateFin: AbstractControl | null;

  let form: FormGroup;

  beforeEach(() => {
    form = new FormGroup(
      {
        dateDebut: new FormControl(),
        dateFin: new FormControl()
      },
      { validators: compareTwoDatesValidator('dateDebut', 'dateFin') }
    );
    dateDebut = form.get('dateDebut');
    dateFin = form.get('dateFin');
  });

  it('retourne une erreur si dateDebut > dateFin', () => {
    dateDebut?.setValue('11-11-2020');
    dateFin?.setValue('11-11-2019');

    console.log(form.errors); // returns null !
    expect(form.hasError('incorrectRangeDate')).toBe(true);
  });
});

My test fails: the form should have an error. Why doesn't my test return an error ?