diff --git a/fxjs/cjs_util_unittest.cpp b/fxjs/cjs_util_unittest.cpp
new file mode 100644
index 0000000..6f43f0f
--- /dev/null
+++ b/fxjs/cjs_util_unittest.cpp
@@ -0,0 +1,113 @@
+// Copyright 2017 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 "fxjs/cjs_util.h"
+
+#include "testing/gtest/include/gtest/gtest.h"
+#include "testing/test_support.h"
+
+TEST(CJS_Util, ParseDataType) {
+  struct ParseDataTypeCase {
+    const wchar_t* const input_string;
+    const int expected;
+  };
+
+  // Commented out tests follow the spec but are not passing.
+  const ParseDataTypeCase cases[] = {
+      // Not conversions
+      {L"", -1},
+      {L"d", -1},
+
+      // Simple cases
+      {L"%d", UTIL_INT},
+      {L"%x", UTIL_INT},
+      {L"%f", UTIL_DOUBLE},
+      {L"%s", UTIL_STRING},
+
+      // nDecSep Not implemented
+      // {L"%,0d", UTIL_INT},
+      // {L"%,1d", UTIL_INT},
+      // {L"%,2d", UTIL_INT},
+      // {L"%,3d", UTIL_INT},
+      // {L"%,4d", -1},
+      // {L"%,d", -1},
+
+      // cFlags("+ 0#"") are only valid for numeric conversions.
+      {L"%+d", UTIL_INT},
+      {L"%+x", UTIL_INT},
+      {L"%+f", UTIL_DOUBLE},
+      // {L"%+s", -1},
+      {L"% d", UTIL_INT},
+      {L"% x", UTIL_INT},
+      {L"% f", UTIL_DOUBLE},
+      // {L"% s", -1},
+      {L"%0d", UTIL_INT},
+      {L"%0x", UTIL_INT},
+      {L"%0f", UTIL_DOUBLE},
+      // {L"%0s", -1},
+      {L"%#d", UTIL_INT},
+      {L"%#x", UTIL_INT},
+      {L"%#f", UTIL_DOUBLE},
+      // {L"%#s", -1},
+
+      // nWidth should work. for all conversions, can be combined with cFlags=0
+      // for numbers.
+      {L"%5d", UTIL_INT},
+      {L"%05d", UTIL_INT},
+      {L"%5x", UTIL_INT},
+      {L"%05x", UTIL_INT},
+      {L"%5f", UTIL_DOUBLE},
+      {L"%05f", UTIL_DOUBLE},
+      {L"%5s", UTIL_STRING},
+      // {L"%05s", -1},
+
+      // nPrecision should only work for float
+      // {L"%.5d", -1},
+      // {L"%.5x", -1},
+      {L"%.5f", UTIL_DOUBLE},
+      // {L"%.5s", -1},
+      // {L"%.14d", -1},
+      // {L"%.14x", -1},
+      {L"%.14f", UTIL_DOUBLE},
+      // {L"%.14s", -1},
+      // {L"%.f", -1},
+
+      // See https://crbug.com/740166
+      // nPrecision too large (> 260) causes crashes in Windows.
+      // Avoid this by limiting to two digits
+      {L"%.1d", UTIL_INT},
+      {L"%.10d", UTIL_INT},
+      {L"%.100d", -1},
+
+      // Unexpected characters
+      {L"%ad", -1},
+      {L"%bx", -1},
+      // {L"%cf", -1},
+      // {L"%es", -1},
+      // {L"%gd", -1},
+      {L"%hx", -1},
+      // {L"%if", -1},
+      {L"%js", -1},
+      {L"%@d", -1},
+      {L"%~x", -1},
+      {L"%[f", -1},
+      {L"%\0s", -1},
+      {L"%\nd", -1},
+      {L"%\rx", -1},
+      // {L"%%f", -1},
+      // {L"%  s", -1},
+
+      // Combine multiple valid components
+      {L"%+6d", UTIL_INT},
+      {L"% 7x", UTIL_INT},
+      {L"%#9.3f", UTIL_DOUBLE},
+      {L"%10s", UTIL_STRING},
+  };
+
+  for (size_t i = 0; i < FX_ArraySize(cases); i++) {
+    std::wstring input(cases[i].input_string);
+    EXPECT_EQ(cases[i].expected, util::ParseDataType(&input))
+        << cases[i].input_string;
+  }
+}