Add a PrintTo function for rtc::Optional to aid with testing.

webrtc/base/optional_unittest.cc

 /*
  *  Copyright 2015 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #include <memory>
 #include <sstream>
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "webrtc/base/gunit.h"
 #include "webrtc/base/optional.h"
 
 namespace rtc {
 
 namespace {
 
+struct MyUnprintableType {
+  int value;
+};
+
+struct MyPrintableType {
+  int value;
+};
+
+struct MyOstreamPrintableType {
+  int value;
+};
+
+// Since only one of these two (PrintTo and operator<<) will be picked by gtest
+// for printing, we need to ensure it's fine that the other one is unused. The
+// test itself will ensure the correct one is called.
+void PrintTo(const MyPrintableType& mpt, std::ostream* os)
+    __attribute__((unused));
+
+void PrintTo(const MyPrintableType& mpt, std::ostream* os) {
+  *os << "The value is " << mpt.value;
+}
+
+std::ostream& operator<<(std::ostream& os,
+                         const MyPrintableType& mpt) __attribute__((unused));
+
+std::ostream& operator<<(std::ostream& os,
+                         const MyPrintableType& mpt) {
+  os << mpt.value;
+  return os;
+}
+
+std::ostream& operator<<(std::ostream& os,
+                         const MyOstreamPrintableType& mpt) {
+  os << mpt.value;
+  return os;
+}
+
 // Class whose instances logs various method calls (constructor, destructor,
 // etc.). Each instance has a unique ID (a simple global sequence number) and
 // an origin ID. When a copy is made, the new object gets a fresh ID but copies
 // the origin ID from the original. When a new Logger is created from scratch,
 // it gets a fresh ID, and the origin ID is the same as the ID (default
 // constructor) or given as an argument (explicit constructor).
 class Logger {
  public:
   Logger() : id_(g_next_id++), origin_(id_) { Log("default constructor"); }
   explicit Logger(int origin) : id_(g_next_id++), origin_(origin) {
@@ skipping 699 matching lines @@
     Logger moved = x.MoveValue();
     log->push_back("---");
   }
   EXPECT_EQ(
       V("0:42. explicit constructor", "1:42. move constructor (from 0:42)",
         "0:42. destructor", "---", "2:42. move constructor (from 1:42)", "---",
         "2:42. destructor", "1:42. destructor"),
       *log);
 }
 
+TEST(OptionalTest, TestPrintTo) {
+  constexpr char kEmptyOptionalMessage[] = "<empty optional>";
+  const Optional<MyUnprintableType> empty_unprintable;
+  const Optional<MyPrintableType> empty_printable;
+  const Optional<MyOstreamPrintableType> empty_ostream_printable;
+  EXPECT_EQ(kEmptyOptionalMessage, ::testing::PrintToString(empty_unprintable));
+  EXPECT_EQ(kEmptyOptionalMessage, ::testing::PrintToString(empty_printable));
+  EXPECT_EQ(kEmptyOptionalMessage,
+            ::testing::PrintToString(empty_ostream_printable));
+  EXPECT_NE("1", ::testing::PrintToString(Optional<MyUnprintableType>({1})));
+  EXPECT_NE("1", ::testing::PrintToString(Optional<MyPrintableType>({1})));
+  EXPECT_EQ("The value is 1",
+            ::testing::PrintToString(Optional<MyPrintableType>({1})));
+  EXPECT_EQ("1",
+            ::testing::PrintToString(Optional<MyOstreamPrintableType>({1})));
+}
+
 }  // namespace rtc