This adds adds four macros when compiling using GTEST_OS_MAC:

testing/gtest_mac.mm

+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "gtest_mac.h"
+
+#include <gtest/internal/gtest-port.h>
+#include <gtest/internal/gtest-string.h>
+#include <gtest/gtest.h>
+
+#ifdef GTEST_OS_MAC
+
+#import <Foundation/Foundation.h>
+
+namespace testing {
+namespace internal {
+
+// This overloaded version allows comparison between ObjC objects that conform
+// to the NSObject protocol. Used to implement {ASSERT|EXPECT}_EQ().
+GTEST_API_ AssertionResult CmpHelperNSEQ(const char* expected_expression,
+                                         const char* actual_expression,
+                                         id<NSObject> expected,
+                                         id<NSObject> actual) {

[Scott Hess - ex-Googler, 2010/08/10 00:00:34]

Suggest you add something like:

  if (!expected && !actual)
    return AssertionSuccess();
  else if (!expected)
    return EqFailure(expected_expr, actual_expr, "<nil>", String(...), false);
  else if (!actual)
    return EqFailure(expected_expr, actual_expr, String(...), "<nil>", false);

Purpose is two-fold, both nil should be treated as eq, and provide a more useful
diagnostic otherwise.  Hmm, and -isEqual:nil might be poor.

+  if ([expected isEqual:actual]) {
+    return AssertionSuccess();
+  }
+  return EqFailure(expected_expression,
+                   actual_expression,
+                   String([[expected description] UTF8String]),
+                   String([[actual description] UTF8String]),
+                   false);
+}
+
+// This overloaded version allows comparison between ObjC objects that conform
+// to the NSObject protocol. Used to implement {ASSERT|EXPECT}_NE().
+GTEST_API_ AssertionResult CmpHelperNSNE(const char* expected_expression,
+                                         const char* actual_expression,
+                                         id<NSObject> expected,
+                                         id<NSObject> actual) {
+  if (![expected isEqual:actual]) {

[Scott Hess - ex-Googler, 2010/08/10 00:00:34]

This isn't right if !expected && !actual.  And likely similar reasoning to above
for better diagnostic output.

+    return AssertionSuccess();
+  }
+  Message msg;
+  msg << "Expected: (" << expected_expression << ") != (" << actual_expression
+      << "), actual: " << String([[expected description] UTF8String])
+      << " vs " << String([[actual description] UTF8String]);
+  return AssertionFailure(msg);
+}
+
+}  // namespace internal
+}  // namespace testing
+
+#endif  // GTEST_OS_MAC