it('should build date range for today', () => {
      var offsetConfig = getDateOffsetConfig('today');
      var range = DynamicDateRange.buildDateRange(offsetConfig);
      expect(range).to.exists;
      expect(range.length).to.equal(2);

      var now = moment();
      expect(now.isBetween(range[0], range[1], null, '[]')).to.be.true;
    });
    it('should build date range for before', () => {
      var offsetConfig = getDateOffsetConfig('before', '5', 'days');
      var range = DynamicDateRange.buildDateRange(offsetConfig);
      expect(range).to.exists;
      expect(range.length).to.equal(2);
      expect(range[0]).to.equal('');

      var end = moment(range[1]);
      var now = moment();
      expect(now.isAfter(end)).to.be.true;
    });
    it('should build date range for last', () => {
      var now = moment();

      var offsetConfig = getDateOffsetConfig('last', '5', 'days');
      var range = DynamicDateRange.buildDateRange(offsetConfig);
      expect(range).to.exists;
      expect(range.length).to.equal(2);

      var start = moment(range[0]);
      var end = moment(range[1]);
      expect(start.isBefore(end)).to.be.true;
      expect(now.isBetween(start, end, null, '(]')).to.be.true;
    });
 it('should build empty date range for unknown date step', () => {
   var offsetConfig = getDateOffsetConfig('uknown-step');
   var range = DynamicDateRange.buildDateRange(offsetConfig);
   expect(range).to.deep.equal(['', '']);
 });