[Mac] Better handling of nil for testing macros.

testing/gtest_mac_unittest.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.
 
 // Note that while this file is in testing/ and tests GTest macros, it is built
 // as part of Chromium's unit_tests target because the project does not build
 // or run GTest's internal test suite.
 
 #import "testing/gtest_mac.h"
 
@@ skipping 27 matching lines @@
   base::mac::ScopedNSAutoreleasePool pool;
 
   EXPECT_NSNE([NSNumber numberWithInt:2], [NSNumber numberWithInt:42]);
 }
 
 TEST(GTestMac, AssertNSNE) {
   base::mac::ScopedNSAutoreleasePool pool;
 
   ASSERT_NSNE(@"a", @"b");
 }
+
+TEST(GTestMac, ExpectNSNil) {
+  base::mac::ScopedNSAutoreleasePool pool;
+
+  EXPECT_NSEQ(nil, nil);
+  EXPECT_NSNE(nil, @"a");
+  EXPECT_NSNE(@"a", nil);
+
+  // TODO(shess): Test that EXPECT_NSNE(nil, nil) fails.
+}