Add Autodiff Codegen Tests

This patch adds end-to-end tests for the autodiff codegen system.
First, code is generated for various functors. This code is then
executed with different arguments and the result is compared
to traditional autodiff.

Change-Id: Icba9996ece26384a795d5b50480ec8194cab572f

internal/ceres/test_util.h

@@ -32,6 +32,7 @@
 #define CERES_INTERNAL_TEST_UTIL_H_
 
 #include <string>
+
 #include "ceres/internal/port.h"
 #include "ceres/problem.h"
 #include "ceres/solver.h"
@@ -44,6 +45,9 @@ namespace internal {
 // Expects that x and y have a relative difference of no more than
 // max_abs_relative_difference. If either x or y is zero, then the relative
 // difference is interpreted as an absolute difference.
+//
+// If x and y have the same non-finite value (inf or nan) we treat them as being
+// close. In such a case no error is thrown and true is returned.
 bool ExpectClose(double x, double y, double max_abs_relative_difference);
 
 // Expects that for all i = 1,.., n - 1
@@ -113,11 +117,8 @@ class SystemTest : public ::testing::Test {
     Solver::Summary summary;
     Solve(options, problem, &summary);
     CHECK_NE(summary.termination_type, ceres::FAILURE);
-    problem->Evaluate(Problem::EvaluateOptions(),
-                      nullptr,
-                      final_residuals,
-                      nullptr,
-                      nullptr);
+    problem->Evaluate(
+        Problem::EvaluateOptions(), nullptr, final_residuals, nullptr, nullptr);
   }
 
   std::vector<double> expected_final_residuals_;