it('should reset minDate to -Infinity when set empty string', function() {
        var elm = compileDirective('options-minDate');
        angular.element(elm[0]).triggerHandler('focus');
        expect(sandboxEl.find('.dropdown-menu tbody button:contains(19)').is(':disabled')).toBeTruthy();
        expect(sandboxEl.find('.dropdown-menu tbody button:contains(20)').is(':disabled')).toBeFalsy();