Implement wide->UTF-8 string conversion more correctly

git-svn-id: http://googletest.googlecode.com/svn/trunk@81 861a406c-534a-0410-8894-cb66d6ee9925

4 files changed, 301 insertions, 66 deletions

diff --git a/include/gtest/internal/gtest-port.h b/include/gtest/internal/gtest-port.h
index 8dbc2d0..5be0d53 100644
--- a/include/gtest/internal/gtest-port.h
+++ b/include/gtest/internal/gtest-port.h
@@ -225,6 +225,12 @@
 #include <sys/mman.h>
 #endif  // GTEST_HAS_STD_STRING && defined(GTEST_OS_LINUX)
 
+// Determines whether the system compiler uses UTF-16 for encoding wide strings.
+#if defined(GTEST_OS_WINDOWS) || defined(GTEST_OS_CYGWIN) || \
+        defined(__SYMBIAN32__)
+#define GTEST_WIDE_STRING_USES_UTF16_ 1
+#endif
+
 // Defines some utility macros.
 
 // The GNU compiler emits a warning if nested "if" statements are followed by
diff --git a/src/gtest-internal-inl.h b/src/gtest-internal-inl.h
index 7757191..2633d69 100644
--- a/src/gtest-internal-inl.h
+++ b/src/gtest-internal-inl.h
@@ -133,8 +133,30 @@ class GTestFlagSaver {
   internal::Int32 repeat_;
 } GTEST_ATTRIBUTE_UNUSED;
 
-// Converts a Unicode code-point to its UTF-8 encoding.
-String ToUtf8String(wchar_t wchar);
+// Converts a Unicode code point to a narrow string in UTF-8 encoding.
+// code_point parameter is of type UInt32 because wchar_t may not be
+// wide enough to contain a code point.
+// The output buffer str must containt at least 32 characters.
+// The function returns the address of the output buffer.
+// If the code_point is not a valid Unicode code point
+// (i.e. outside of Unicode range U+0 to U+10FFFF) it will be output
+// as '(Invalid Unicode 0xXXXXXXXX)'.
+char* CodePointToUtf8(UInt32 code_point, char* str);
+
+// Converts a wide string to a narrow string in UTF-8 encoding.
+// The wide string is assumed to have the following encoding:
+//   UTF-16 if sizeof(wchar_t) == 2 (on Windows, Cygwin, Symbian OS)
+//   UTF-32 if sizeof(wchar_t) == 4 (on Linux)
+// Parameter str points to a null-terminated wide string.
+// Parameter num_chars may additionally limit the number
+// of wchar_t characters processed. -1 is used when the entire string
+// should be processed.
+// If the string contains code points that are not valid Unicode code points
+// (i.e. outside of Unicode range U+0 to U+10FFFF) they will be output
+// as '(Invalid Unicode 0xXXXXXXXX)'. If the string is in UTF16 encoding
+// and contains invalid UTF-16 surrogate pairs, values in those pairs
+// will be encoded as individual Unicode characters from Basic Normal Plane.
+String WideStringToUtf8(const wchar_t* str, int num_chars);
 
 // Returns the number of active threads, or 0 when there is an error.
 size_t GetThreadCount();
diff --git a/src/gtest.cc b/src/gtest.cc
index a0a0520..740eb74 100644
--- a/src/gtest.cc
+++ b/src/gtest.cc
@@ -784,16 +784,19 @@ bool String::CStringEquals(const char * lhs, const char * rhs) {
 // encoding, and streams the result to the given Message object.
 static void StreamWideCharsToMessage(const wchar_t* wstr, size_t len,
                                      Message* msg) {
-  for (size_t i = 0; i != len; i++) {
-    // TODO(wan): consider allowing a testing::String object to
-    // contain '\0'.  This will make it behave more like std::string,
-    // and will allow ToUtf8String() to return the correct encoding
-    // for '\0' s.t. we can get rid of the conditional here (and in
-    // several other places).
-    if (wstr[i]) {
-      *msg << internal::ToUtf8String(wstr[i]);
+  // TODO(wan): consider allowing a testing::String object to
+  // contain '\0'.  This will make it behave more like std::string,
+  // and will allow ToUtf8String() to return the correct encoding
+  // for '\0' s.t. we can get rid of the conditional here (and in
+  // several other places).
+  for (size_t i = 0; i != len; ) {  // NOLINT
+    if (wstr[i] != L'\0') {
+      *msg << WideStringToUtf8(wstr + i, len - i);
+      while (i != len && wstr[i] != L'\0')
+        i++;
     } else {
       *msg << '\0';
+      i++;
     }
   }
 }
@@ -852,8 +855,10 @@ String FormatForFailureMessage(wchar_t wchar) {
   Message msg;
   // A String object cannot contain '\0', so we print "\\0" when wchar is
   // L'\0'.
-  msg << "L'" << (wchar ? ToUtf8String(wchar).c_str() : "\\0") << "' ("
-      << wchar_as_uint64 << ", 0x" << ::std::setbase(16)
+  char buffer[32];  // CodePointToUtf8 requires a buffer that big.
+  msg << "L'"
+      << (wchar ? CodePointToUtf8(static_cast<UInt32>(wchar), buffer) : "\\0")
+      << "' (" << wchar_as_uint64 << ", 0x" << ::std::setbase(16)
       << wchar_as_uint64 << ")";
   return msg.GetString();
 }
@@ -1317,31 +1322,118 @@ inline UInt32 ChopLowBits(UInt32* bits, int n) {
   return low_bits;
 }
 
-// Converts a Unicode code-point to its UTF-8 encoding.
-String ToUtf8String(wchar_t wchar) {
-  char str[5] = {};  // Initializes str to all '\0' characters.
-
-  UInt32 code = static_cast<UInt32>(wchar);
-  if (code <= kMaxCodePoint1) {
-    str[0] = static_cast<char>(code);                          // 0xxxxxxx
-  } else if (code <= kMaxCodePoint2) {
-    str[1] = static_cast<char>(0x80 | ChopLowBits(&code, 6));  // 10xxxxxx
-    str[0] = static_cast<char>(0xC0 | code);                   // 110xxxxx
-  } else if (code <= kMaxCodePoint3) {
-    str[2] = static_cast<char>(0x80 | ChopLowBits(&code, 6));  // 10xxxxxx
-    str[1] = static_cast<char>(0x80 | ChopLowBits(&code, 6));  // 10xxxxxx
-    str[0] = static_cast<char>(0xE0 | code);                   // 1110xxxx
-  } else if (code <= kMaxCodePoint4) {
-    str[3] = static_cast<char>(0x80 | ChopLowBits(&code, 6));  // 10xxxxxx
-    str[2] = static_cast<char>(0x80 | ChopLowBits(&code, 6));  // 10xxxxxx
-    str[1] = static_cast<char>(0x80 | ChopLowBits(&code, 6));  // 10xxxxxx
-    str[0] = static_cast<char>(0xF0 | code);                   // 11110xxx
+// Converts a Unicode code point to a narrow string in UTF-8 encoding.
+// code_point parameter is of type UInt32 because wchar_t may not be
+// wide enough to contain a code point.
+// The output buffer str must containt at least 32 characters.
+// The function returns the address of the output buffer.
+// If the code_point is not a valid Unicode code point
+// (i.e. outside of Unicode range U+0 to U+10FFFF) it will be output
+// as '(Invalid Unicode 0xXXXXXXXX)'.
+char* CodePointToUtf8(UInt32 code_point, char* str) {
+  if (code_point <= kMaxCodePoint1) {
+    str[1] = '\0';
+    str[0] = static_cast<char>(code_point);                          // 0xxxxxxx
+  } else if (code_point <= kMaxCodePoint2) {
+    str[2] = '\0';
+    str[1] = static_cast<char>(0x80 | ChopLowBits(&code_point, 6));  // 10xxxxxx
+    str[0] = static_cast<char>(0xC0 | code_point);                   // 110xxxxx
+  } else if (code_point <= kMaxCodePoint3) {
+    str[3] = '\0';
+    str[2] = static_cast<char>(0x80 | ChopLowBits(&code_point, 6));  // 10xxxxxx
+    str[1] = static_cast<char>(0x80 | ChopLowBits(&code_point, 6));  // 10xxxxxx
+    str[0] = static_cast<char>(0xE0 | code_point);                   // 1110xxxx
+  } else if (code_point <= kMaxCodePoint4) {
+    str[4] = '\0';
+    str[3] = static_cast<char>(0x80 | ChopLowBits(&code_point, 6));  // 10xxxxxx
+    str[2] = static_cast<char>(0x80 | ChopLowBits(&code_point, 6));  // 10xxxxxx
+    str[1] = static_cast<char>(0x80 | ChopLowBits(&code_point, 6));  // 10xxxxxx
+    str[0] = static_cast<char>(0xF0 | code_point);                   // 11110xxx
   } else {
-    return String::Format("(Invalid Unicode 0x%llX)",
-                          static_cast<UInt64>(wchar));
+    // The longest string String::Format can produce when invoked
+    // with these parameters is 28 character long (not including
+    // the terminating nul character). We are asking for 32 character
+    // buffer just in case. This is also enough for strncpy to
+    // null-terminate the destination string.
+    // MSVC 8 deprecates strncpy(), so we want to suppress warning
+    // 4996 (deprecated function) there.
+#ifdef GTEST_OS_WINDOWS  // We are on Windows.
+#pragma warning(push)          // Saves the current warning state.
+#pragma warning(disable:4996)  // Temporarily disables warning 4996.
+#endif
+    strncpy(str, String::Format("(Invalid Unicode 0x%X)", code_point).c_str(),
+            32);
+#ifdef GTEST_OS_WINDOWS  // We are on Windows.
+#pragma warning(pop)           // Restores the warning state.
+#endif
+    str[31] = '\0';  // Makes sure no change in the format to strncpy leaves
+                     // the result unterminated.
   }
+  return str;
+}
+
+// The following two functions only make sense if the the system
+// uses UTF-16 for wide string encoding. All supported systems
+// with 16 bit wchar_t (Windows, Cygwin, Symbian OS) do use UTF-16.
 
-  return String(str);
+// Determines if the arguments constitute UTF-16 surrogate pair
+// and thus should be combined into a single Unicode code point
+// using CreateCodePointFromUtf16SurrogatePair.
+inline bool IsUtf16SurrogatePair(wchar_t first, wchar_t second) {
+  if (sizeof(wchar_t) == 2)
+    return (first & 0xFC00) == 0xD800 && (second & 0xFC00) == 0xDC00;
+  else
+    return false;
+}
+
+// Creates a Unicode code point from UTF16 surrogate pair.
+inline UInt32 CreateCodePointFromUtf16SurrogatePair(wchar_t first,
+                                                    wchar_t second) {
+  if (sizeof(wchar_t) == 2) {
+    const UInt32 mask = (1 << 10) - 1;
+    return (((first & mask) << 10) | (second & mask)) + 0x10000;
+  } else {
+    // This should not be called, but we provide a sensible default
+    // in case it is.
+    return static_cast<UInt32>(first);
+  }
+}
+
+// Converts a wide string to a narrow string in UTF-8 encoding.
+// The wide string is assumed to have the following encoding:
+//   UTF-16 if sizeof(wchar_t) == 2 (on Windows, Cygwin, Symbian OS)
+//   UTF-32 if sizeof(wchar_t) == 4 (on Linux)
+// Parameter str points to a null-terminated wide string.
+// Parameter num_chars may additionally limit the number
+// of wchar_t characters processed. -1 is used when the entire string
+// should be processed.
+// If the string contains code points that are not valid Unicode code points
+// (i.e. outside of Unicode range U+0 to U+10FFFF) they will be output
+// as '(Invalid Unicode 0xXXXXXXXX)'. If the string is in UTF16 encoding
+// and contains invalid UTF-16 surrogate pairs, values in those pairs
+// will be encoded as individual Unicode characters from Basic Normal Plane.
+String WideStringToUtf8(const wchar_t* str, int num_chars) {
+  if (num_chars == -1)
+    num_chars = wcslen(str);
+
+  StrStream stream;
+  for (int i = 0; i < num_chars; ++i) {
+    UInt32 unicode_code_point;
+
+    if (str[i] == L'\0') {
+      break;
+    } else if (i + 1 < num_chars && IsUtf16SurrogatePair(str[i], str[i + 1])) {
+      unicode_code_point = CreateCodePointFromUtf16SurrogatePair(str[i],
+                                                                 str[i + 1]);
+      i++;
+    } else {
+      unicode_code_point = static_cast<UInt32>(str[i]);
+    }
+
+    char buffer[32];  // CodePointToUtf8 requires a buffer this big.
+    stream << CodePointToUtf8(unicode_code_point, buffer);
+  }
+  return StrStreamToString(&stream);
 }
 
 // Converts a wide C string to a String using the UTF-8 encoding.
@@ -1349,12 +1441,7 @@ String ToUtf8String(wchar_t wchar) {
 String String::ShowWideCString(const wchar_t * wide_c_str) {
   if (wide_c_str == NULL) return String("(null)");
 
-  StrStream ss;
-  while (*wide_c_str) {
-    ss << internal::ToUtf8String(*wide_c_str++);
-  }
-
-  return internal::StrStreamToString(&ss);
+  return String(internal::WideStringToUtf8(wide_c_str, -1).c_str());
 }
 
 // Similar to ShowWideCString(), except that this function encloses
diff --git a/test/gtest_unittest.cc b/test/gtest_unittest.cc
index 9f1cbe9..eecaf4e 100644
--- a/test/gtest_unittest.cc
+++ b/test/gtest_unittest.cc
@@ -101,6 +101,7 @@ using testing::TPRT_NONFATAL_FAILURE;
 using testing::TPRT_SUCCESS;
 using testing::UnitTest;
 using testing::internal::AppendUserMessage;
+using testing::internal::CodePointToUtf8;
 using testing::internal::EqFailure;
 using testing::internal::FloatingPoint;
 using testing::internal::GTestFlagSaver;
@@ -111,8 +112,8 @@ using testing::internal::StreamableToString;
 using testing::internal::String;
 using testing::internal::TestProperty;
 using testing::internal::TestResult;
-using testing::internal::ToUtf8String;
 using testing::internal::UnitTestImpl;
+using testing::internal::WideStringToUtf8;
 
 // This line tests that we can define tests in an unnamed namespace.
 namespace {
@@ -142,65 +143,184 @@ TEST(NullLiteralTest, IsFalseForNonNullLiterals) {
 }
 
 #endif  // __SYMBIAN32__
-// Tests ToUtf8String().
+//
+// Tests CodePointToUtf8().
 
 // Tests that the NUL character L'\0' is encoded correctly.
-TEST(ToUtf8StringTest, CanEncodeNul) {
-  EXPECT_STREQ("", ToUtf8String(L'\0').c_str());
+TEST(CodePointToUtf8Test, CanEncodeNul) {
+  char buffer[32];
+  EXPECT_STREQ("", CodePointToUtf8(L'\0', buffer));
 }
 
 // Tests that ASCII characters are encoded correctly.
-TEST(ToUtf8StringTest, CanEncodeAscii) {
-  EXPECT_STREQ("a", ToUtf8String(L'a').c_str());
-  EXPECT_STREQ("Z", ToUtf8String(L'Z').c_str());
-  EXPECT_STREQ("&", ToUtf8String(L'&').c_str());
-  EXPECT_STREQ("\x7F", ToUtf8String(L'\x7F').c_str());
+TEST(CodePointToUtf8Test, CanEncodeAscii) {
+  char buffer[32];
+  EXPECT_STREQ("a", CodePointToUtf8(L'a', buffer));
+  EXPECT_STREQ("Z", CodePointToUtf8(L'Z', buffer));
+  EXPECT_STREQ("&", CodePointToUtf8(L'&', buffer));
+  EXPECT_STREQ("\x7F", CodePointToUtf8(L'\x7F', buffer));
 }
 
 // Tests that Unicode code-points that have 8 to 11 bits are encoded
 // as 110xxxxx 10xxxxxx.
-TEST(ToUtf8StringTest, CanEncode8To11Bits) {
+TEST(CodePointToUtf8Test, CanEncode8To11Bits) {
+  char buffer[32];
   // 000 1101 0011 => 110-00011 10-010011
-  EXPECT_STREQ("\xC3\x93", ToUtf8String(L'\xD3').c_str());
+  EXPECT_STREQ("\xC3\x93", CodePointToUtf8(L'\xD3', buffer));
 
   // 101 0111 0110 => 110-10101 10-110110
-  EXPECT_STREQ("\xD5\xB6", ToUtf8String(L'\x576').c_str());
+  EXPECT_STREQ("\xD5\xB6", CodePointToUtf8(L'\x576', buffer));
 }
 
 // Tests that Unicode code-points that have 12 to 16 bits are encoded
 // as 1110xxxx 10xxxxxx 10xxxxxx.
-TEST(ToUtf8StringTest, CanEncode12To16Bits) {
+TEST(CodePointToUtf8Test, CanEncode12To16Bits) {
+  char buffer[32];
   // 0000 1000 1101 0011 => 1110-0000 10-100011 10-010011
-  EXPECT_STREQ("\xE0\xA3\x93", ToUtf8String(L'\x8D3').c_str());
+  EXPECT_STREQ("\xE0\xA3\x93", CodePointToUtf8(L'\x8D3', buffer));
 
   // 1100 0111 0100 1101 => 1110-1100 10-011101 10-001101
-  EXPECT_STREQ("\xEC\x9D\x8D", ToUtf8String(L'\xC74D').c_str());
+  EXPECT_STREQ("\xEC\x9D\x8D", CodePointToUtf8(L'\xC74D', buffer));
 }
 
-#if !defined(GTEST_OS_WINDOWS) && !defined(GTEST_OS_CYGWIN) && \
-    !defined(__SYMBIAN32__)
-
+#ifndef GTEST_WIDE_STRING_USES_UTF16_
 // Tests in this group require a wchar_t to hold > 16 bits, and thus
 // are skipped on Windows, Cygwin, and Symbian, where a wchar_t is
-// 16-bit wide.
+// 16-bit wide. This code may not compile on those systems.
 
 // Tests that Unicode code-points that have 17 to 21 bits are encoded
 // as 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx.
-TEST(ToUtf8StringTest, CanEncode17To21Bits) {
+TEST(CodePointToUtf8Test, CanEncode17To21Bits) {
+  char buffer[32];
   // 0 0001 0000 1000 1101 0011 => 11110-000 10-010000 10-100011 10-010011
-  EXPECT_STREQ("\xF0\x90\xA3\x93", ToUtf8String(L'\x108D3').c_str());
+  EXPECT_STREQ("\xF0\x90\xA3\x93", CodePointToUtf8(L'\x108D3', buffer));
+
+  // 0 0001 0000 0100 0000 0000 => 11110-000 10-010000 10-010000 10-000000
+  EXPECT_STREQ("\xF0\x90\x90\x80", CodePointToUtf8(L'\x10400', buffer));
 
-  // 1 0111 1000 0110 0011 0100 => 11110-101 10-111000 10-011000 10-110100
-  EXPECT_STREQ("\xF5\xB8\x98\xB4", ToUtf8String(L'\x178634').c_str());
+  // 1 0000 1000 0110 0011 0100 => 11110-100 10-001000 10-011000 10-110100
+  EXPECT_STREQ("\xF4\x88\x98\xB4", CodePointToUtf8(L'\x108634', buffer));
 }
 
 // Tests that encoding an invalid code-point generates the expected result.
-TEST(ToUtf8StringTest, CanEncodeInvalidCodePoint) {
+TEST(CodePointToUtf8Test, CanEncodeInvalidCodePoint) {
+  char buffer[32];
   EXPECT_STREQ("(Invalid Unicode 0x1234ABCD)",
-               ToUtf8String(L'\x1234ABCD').c_str());
+               CodePointToUtf8(L'\x1234ABCD', buffer));
+}
+
+#endif  // GTEST_WIDE_STRING_USES_UTF16_
+
+// Tests WideStringToUtf8().
+
+// Tests that the NUL character L'\0' is encoded correctly.
+TEST(WideStringToUtf8Test, CanEncodeNul) {
+  EXPECT_STREQ("", WideStringToUtf8(L"", 0).c_str());
+  EXPECT_STREQ("", WideStringToUtf8(L"", -1).c_str());
+}
+
+// Tests that ASCII strings are encoded correctly.
+TEST(WideStringToUtf8Test, CanEncodeAscii) {
+  EXPECT_STREQ("a", WideStringToUtf8(L"a", 1).c_str());
+  EXPECT_STREQ("ab", WideStringToUtf8(L"ab", 2).c_str());
+  EXPECT_STREQ("a", WideStringToUtf8(L"a", -1).c_str());
+  EXPECT_STREQ("ab", WideStringToUtf8(L"ab", -1).c_str());
+}
+
+// Tests that Unicode code-points that have 8 to 11 bits are encoded
+// as 110xxxxx 10xxxxxx.
+TEST(WideStringToUtf8Test, CanEncode8To11Bits) {
+  // 000 1101 0011 => 110-00011 10-010011
+  EXPECT_STREQ("\xC3\x93", WideStringToUtf8(L"\xD3", 1).c_str());
+  EXPECT_STREQ("\xC3\x93", WideStringToUtf8(L"\xD3", -1).c_str());
+
+  // 101 0111 0110 => 110-10101 10-110110
+  EXPECT_STREQ("\xD5\xB6", WideStringToUtf8(L"\x576", 1).c_str());
+  EXPECT_STREQ("\xD5\xB6", WideStringToUtf8(L"\x576", -1).c_str());
+}
+
+// Tests that Unicode code-points that have 12 to 16 bits are encoded
+// as 1110xxxx 10xxxxxx 10xxxxxx.
+TEST(WideStringToUtf8Test, CanEncode12To16Bits) {
+  // 0000 1000 1101 0011 => 1110-0000 10-100011 10-010011
+  EXPECT_STREQ("\xE0\xA3\x93", WideStringToUtf8(L"\x8D3", 1).c_str());
+  EXPECT_STREQ("\xE0\xA3\x93", WideStringToUtf8(L"\x8D3", -1).c_str());
+
+  // 1100 0111 0100 1101 => 1110-1100 10-011101 10-001101
+  EXPECT_STREQ("\xEC\x9D\x8D", WideStringToUtf8(L"\xC74D", 1).c_str());
+  EXPECT_STREQ("\xEC\x9D\x8D", WideStringToUtf8(L"\xC74D", -1).c_str());
 }
 
-#endif  // Windows, Cygwin, or Symbian
+// Tests that the conversion stops when the function encounters \0 character.
+TEST(WideStringToUtf8Test, StopsOnNulCharacter) {
+  EXPECT_STREQ("ABC", WideStringToUtf8(L"ABC\0XYZ", 100).c_str());
+}
+
+// Tests that the conversion stops when the function reaches the limit
+// specified by the 'length' parameter.
+TEST(WideStringToUtf8Test, StopsWhenLengthLimitReached) {
+  EXPECT_STREQ("ABC", WideStringToUtf8(L"ABCDEF", 3).c_str());
+}
+
+
+#ifndef GTEST_WIDE_STRING_USES_UTF16_
+// Tests that Unicode code-points that have 17 to 21 bits are encoded
+// as 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx. This code may not compile
+// on the systems using UTF-16 encoding.
+TEST(WideStringToUtf8Test, CanEncode17To21Bits) {
+  // 0 0001 0000 1000 1101 0011 => 11110-000 10-010000 10-100011 10-010011
+  EXPECT_STREQ("\xF0\x90\xA3\x93", WideStringToUtf8(L"\x108D3", 1).c_str());
+  EXPECT_STREQ("\xF0\x90\xA3\x93", WideStringToUtf8(L"\x108D3", -1).c_str());
+
+  // 1 0000 1000 0110 0011 0100 => 11110-100 10-001000 10-011000 10-110100
+  EXPECT_STREQ("\xF4\x88\x98\xB4", WideStringToUtf8(L"\x108634", 1).c_str());
+  EXPECT_STREQ("\xF4\x88\x98\xB4", WideStringToUtf8(L"\x108634", -1).c_str());
+}
+
+// Tests that encoding an invalid code-point generates the expected result.
+TEST(WideStringToUtf8Test, CanEncodeInvalidCodePoint) {
+  EXPECT_STREQ("(Invalid Unicode 0xABCDFF)",
+               WideStringToUtf8(L"\xABCDFF", -1).c_str());
+}
+#else
+// Tests that surrogate pairs are encoded correctly on the systems using
+// UTF-16 encoding in the wide strings.
+TEST(WideStringToUtf8Test, CanEncodeValidUtf16SUrrogatePairs) {
+  EXPECT_STREQ("\xF0\x90\x90\x80",
+               WideStringToUtf8(L"\xD801\xDC00", -1).c_str());
+}
+
+// Tests that encoding an invalid UTF-16 surrogate pair
+// generates the expected result.
+TEST(WideStringToUtf8Test, CanEncodeInvalidUtf16SurrogatePair) {
+  // Leading surrogate is at the end of the string.
+  EXPECT_STREQ("\xED\xA0\x80", WideStringToUtf8(L"\xD800", -1).c_str());
+  // Leading surrogate is not followed by the trailing surrogate.
+  EXPECT_STREQ("\xED\xA0\x80$", WideStringToUtf8(L"\xD800$", -1).c_str());
+  // Trailing surrogate appearas without a leading surrogate.
+  EXPECT_STREQ("\xED\xB0\x80PQR", WideStringToUtf8(L"\xDC00PQR", -1).c_str());
+}
+#endif  // GTEST_WIDE_STRING_USES_UTF16_
+
+// Tests that codepoint concatenation works correctly.
+#ifndef GTEST_WIDE_STRING_USES_UTF16_
+TEST(WideStringToUtf8Test, ConcatenatesCodepointsCorrectly) {
+  EXPECT_STREQ(
+      "\xF4\x88\x98\xB4"
+          "\xEC\x9D\x8D"
+          "\n"
+          "\xD5\xB6"
+          "\xE0\xA3\x93"
+          "\xF4\x88\x98\xB4",
+      WideStringToUtf8(L"\x108634\xC74D\n\x576\x8D3\x108634", -1).c_str());
+}
+#else
+TEST(WideStringToUtf8Test, ConcatenatesCodepointsCorrectly) {
+  EXPECT_STREQ(
+      "\xEC\x9D\x8D" "\n" "\xD5\xB6" "\xE0\xA3\x93",
+      WideStringToUtf8(L"\xC74D\n\x576\x8D3", -1).c_str());
+}
+#endif  // GTEST_WIDE_STRING_USES_UTF16_
 
 // Tests the List template class.