Elisabeth DeCoursey and Scott Martens have revitalized a 119-year-old Kansas City company. There are few small businesses with histories as long as Kansas City Testing & Engineering’s.The owners, Elisabeth DeCoursey and Scott Martens, bought the business in 2009, when it was still part of Tetra Tech, a national consulting, construction and engineering firm. Tetra Tech was planning to shut down the unit—until the married couple offered to take it over.One…