it("should not include controls that have no errors", () => {
        var one = new Control("one", validator("a", true));
        var two = new Control("two");
        var g = new ControlGroup({"one": one, "two": two});

        expect(Validators.group(g)).toEqual({"a": [one]});
      });

      it("should ignore nulls", fakeAsync(() => {
           var c = Validators.composeAsync([asyncValidator("expected", {"one": true}), null]);

           var value = null;
           c(new Control("invalid")).then(v => value = v);

           tick(1);

           expect(value).toEqual({"one": true});
         }));

 it("should return null when no errors", () => {
   var c = Validators.compose([Validators.nullValidator, Validators.nullValidator]);
   expect(c(new Control(""))).toEqual(null);
 });

 () => { expect(Validators.compose(null)).toBe(Validators.nullValidator); });