How to use the @aurelia/validation.LengthRule function in @aurelia/validation

it(`LengthRule#execute validates ${value} to be ${isValid} for length constraint ${length}`, function () {
      const sut = new LengthRule((void 0)!, length, isMax);
      assert.equal(sut.messageKey, isMax ? 'maxLength' : 'minLength');
      assert.equal(sut.execute(value), isValid);
    })
  );

      getRule: (sut: IValidationMessageProvider) => new LengthRule(sut, 42, true),
    },

      getRule: (sut: IValidationMessageProvider) => new LengthRule(sut, 42, false),
    },