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

tests/html/utils.dart

 library TestUtils;
 import '../../pkg/unittest/lib/unittest.dart';
 
 /**
  * Verifies that [actual] has the same graph structure as [expected].
  * Detects cycles and DAG structure in Maps and Lists.
  */
 verifyGraph(expected, actual) {
   var eItems = [];
   var aItems = [];
 
   message(path, reason) => path == ''
       ? reason
       : reason == null ? "path: $path" : "path: $path, $reason";
 
   walk(path, expected, actual) {
     if (expected is String || expected is num || expected == null) {
       expect(actual, equals(expected), reason: message(path, 'not equal'));
       return;
     }
 
     // Cycle or DAG?
     for (int i = 0; i < eItems.length; i++) {
-      if (expected === eItems[i]) {
+      if (identical(expected, eItems[i])) {
         expect(actual, same(aItems[i]),
             reason: message(path, 'missing back or side edge'));
         return;
       }
     }
     for (int i = 0; i < aItems.length; i++) {
-      if (actual === aItems[i]) {
+      if (identical(actual, aItems[i])) {
         expect(expected, same(eItems[i]),
             reason: message(path, 'extra back or side edge'));
         return;
       }
     }
     eItems.add(expected);
     aItems.add(actual);
 
     if (expected is List) {
       expect(actual, isList, reason: message(path, '$actual is List'));
@@ skipping 19 matching lines @@
         }
       }
       return;
     }
 
     expect(false, isTrue, reason: 'Unhandled type: $expected');
   }
 
   walk('', expected, actual);
 }