tests/cpp: Add tests for regression_obj.cc

Test the objective functions in regression_obj.cc

tests/cpp: Add tests for objective.cc and RegLossObj

tests/cpp/helpers.h

@@ -5,11 +5,15 @@
 #include <fstream>
 #include <cstdio>
 #include <string>
+#include <vector>
 #include <sys/stat.h>
 #include <sys/types.h>
 
 #include <gtest/gtest.h>
 
+#include <xgboost/base.h>
+#include <xgboost/objective.h>
+
 std::string TempFileName();
 
 bool FileExists(const std::string name);
@@ -18,4 +22,11 @@ long GetFileSize(const std::string filename);
 
 std::string CreateSimpleTestData();
 
+void CheckObjFunction(xgboost::ObjFunction * obj,
+                      std::vector<xgboost::bst_float> preds,
+                      std::vector<xgboost::bst_float> labels,
+                      std::vector<xgboost::bst_float> weights,
+                      std::vector<xgboost::bst_float> out_grad,
+                      std::vector<xgboost::bst_float> out_hess);
+
 #endif