[Sketcher][test] Create test for getConstraintAfterDeletingGeo+

[Sketcher] Add null case to constraint change on deletion checks

src/Mod/Sketcher/App/SketchObject.h

@@ -982,6 +982,8 @@ protected:
                      int thirdGeoId = GeoEnum::GeoUndef,
                      Sketcher::PointPos thirdPos = Sketcher::PointPos::none);
 
+public:
+    // FIXME: These may not need to be public. Decide before merging.
     std::unique_ptr<Constraint> getConstraintAfterDeletingGeo(const Constraint* constr,
                                                               const int deletedGeoId) const;