a === b -> identical(a, b)

tests/compiler/dart2js/dart_backend_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:uri';
 import 'parser_helper.dart';
 import 'mock_compiler.dart';
 import '../../../sdk/lib/_internal/compiler/compiler.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart' as leg;
 import '../../../sdk/lib/_internal/compiler/implementation/dart_backend/dart_backend.dart';
@@ skipping 42 matching lines @@
 ''';
 
 const helperLib = r'''
 #library('js_helper');
 class JSInvocationMirror {}
 ''';
 
 testDart2Dart(String src, {void continuation(String s), bool minify: false,
     bool stripTypes: false}) {
   // If continuation is not provided, check that source string remains the same.
-  if (continuation === null) {
+  if (continuation == null) {
     continuation = (s) { Expect.equals(src, s); };
   }
   testDart2DartWithLibrary(src, '', continuation: continuation, minify: minify,
       stripTypes: stripTypes);
 }
 
 /**
  * Library name is assumed to be 'mylib' in 'mylib.dart' file.
  */
 testDart2DartWithLibrary(
@@ skipping 12 matching lines @@
     }
     if (uri.path.endsWith('/core.dart')) return new Future.immediate(coreLib);
     if (uri.path.endsWith('/io.dart')) return new Future.immediate(ioLib);
     if (uri.path.endsWith('/js_helper.dart')) return new Future.immediate(helperLib);
     // TODO(smok): The file should change to html_dartium at some point.
     if (uri.path.endsWith('/html_dart2js.dart')) return new Future.immediate(htmlLib);
     return new Future.immediate('');
   }
 
   handler(uri, begin, end, message, kind) {
-    if (kind === Diagnostic.ERROR || kind === Diagnostic.CRASH) {
+    if (identical(kind, Diagnostic.ERROR) || identical(kind, Diagnostic.CRASH)) {
       Expect.fail('$uri: $begin-$end: $message [$kind]');
     }
   }
 
   final options = <String>['--output-type=dart'];
   if (minify) options.add('--minify');
   if (stripTypes) options.add('--force-strip=types');
 
   compile(
       scriptUri,
@@ skipping 609 matching lines @@
   testDoubleMains();
   testStaticAccessIoLib();
   testLocalFunctionPlaceholder();
   testMinification();
   testClosureLocalsMinified();
   testParametersMinified();
   testDeclarationTypePlaceholders();
   testPlatformLibraryMemberNamesAreFixed();
   testConflictsWithCoreLib();
 }