Class interval { public: // // an interval is a period of time beginning with a starting time // and running up to, but not including, its stop time. // interval (); interval (datetime start, datetime stop); interval (datetime start, duration length); datetime getstart() const; void setstart (datetime); datetime getstop() const; void setstop (datetime); duration getduration(); bool contains (datetime d); bool overlaps (interval intrvl); bool operator== (const interval& other) const; private: datetime thestart, thestop; }; using the junit style, write a self-checking test for the setstop function.