Compare with a meaningful result

src/test-gradient-method.cc

@@ -474,7 +474,7 @@ void testSteepFunction() {
   start[1] = 0;
 
   double const ret3 = functionTester(J, start, 1);
-  assert(std::abs(ret1 - ret3) < 1e-5);
+  assert(std::abs(ret2 - ret3) < 1e-5);
 }
 
 int main() {