diff --git a/BUILD.gn b/BUILD.gn
index 06c4101..f577986 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -230,6 +230,8 @@
 static_library("test_support") {
   testonly = true
   sources = [
+    "testing/fx_string_testhelpers.cpp",
+    "testing/fx_string_testhelpers.h",
     "testing/test_support.cpp",
     "testing/test_support.h",
     "testing/utils/path_service.cpp",
diff --git a/testing/fx_string_testhelpers.cpp b/testing/fx_string_testhelpers.cpp
new file mode 100644
index 0000000..443cc89
--- /dev/null
+++ b/testing/fx_string_testhelpers.cpp
@@ -0,0 +1,18 @@
+// Copyright 2014 PDFium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "testing/fx_string_testhelpers.h"
+
+#include <iomanip>
+#include <ios>
+#include <string>
+
+std::ostream& operator<<(std::ostream& os, const CFX_DateTime& dt) {
+  os << dt.GetYear() << "-" << std::to_string(dt.GetMonth()) << "-"
+     << std::to_string(dt.GetDay()) << " " << std::to_string(dt.GetHour())
+     << ":" << std::to_string(dt.GetMinute()) << ":"
+     << std::to_string(dt.GetSecond()) << "."
+     << std::to_string(dt.GetMillisecond());
+  return os;
+}
diff --git a/testing/fx_string_testhelpers.h b/testing/fx_string_testhelpers.h
new file mode 100644
index 0000000..34ac69d
--- /dev/null
+++ b/testing/fx_string_testhelpers.h
@@ -0,0 +1,15 @@
+// Copyright 2014 PDFium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef TESTING_FX_STRING_TESTHELPERS_H_
+#define TESTING_FX_STRING_TESTHELPERS_H_
+
+#include <ostream>
+
+#include "core/fxcrt/cfx_datetime.h"
+
+// Output stream operator so GTEST macros work with CFX_DateTime objects.
+std::ostream& operator<<(std::ostream& os, const CFX_DateTime& dt);
+
+#endif  // TESTING_FX_STRING_TESTHELPERS_H_
diff --git a/xfa/fgas/crt/cfgas_formatstring_unittest.cpp b/xfa/fgas/crt/cfgas_formatstring_unittest.cpp
index 2af1507..3adcedf 100644
--- a/xfa/fgas/crt/cfgas_formatstring_unittest.cpp
+++ b/xfa/fgas/crt/cfgas_formatstring_unittest.cpp
@@ -11,6 +11,7 @@
 #include <memory>
 
 #include "core/fpdfapi/cpdf_modulemgr.h"
+#include "testing/fx_string_testhelpers.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/test_support.h"
 #include "third_party/base/ptr_util.h"