Add a more meaningful assertion

src/bisection-simpler-example2-gradient.cc

@@ -12,6 +12,7 @@
 #include <dune/tnnmg/problem-classes/bisection.hh>
 
 #include <cassert>
+#include <cstdlib>
 #include <limits>
 
 template <int dimension>
@@ -125,6 +126,7 @@ int main() {
   start *= 17;
   SampleFunctional::SmallVector correction = J.minimise(start, 20);
   assert(J(start + correction) <= J(start));
+  assert(std::abs(J(start + correction) + 0.833333) < 1e-6);
   std::cout << J(start + correction) << std::endl;
 
   return 0;