Adding isNotEmpty property to collection and string.

tests/corelib/set_test.dart

 // Copyright (c) 2011, 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.
 
 library set_test;
 
 
 import 'package:expect/expect.dart';
 import "dart:collection";
 
 void testMain(Set create()) {
   Set set = create();
-  Expect.equals(0, set.length);
+  testLength(0, set);
   set.add(1);
-  Expect.equals(1, set.length);
+  testLength(1, set);
   Expect.isTrue(set.contains(1));
 
   set.add(1);
-  Expect.equals(1, set.length);
+  testLength(1, set);
   Expect.isTrue(set.contains(1));
 
   set.remove(1);
-  Expect.equals(0, set.length);
+  testLength(0, set);
   Expect.isFalse(set.contains(1));
 
   for (int i = 0; i < 10; i++) {
     set.add(i);
   }
 
-  Expect.equals(10, set.length);
+  testLength(10, set);
   for (int i = 0; i < 10; i++) {
     Expect.isTrue(set.contains(i));
   }
 
-  Expect.equals(10, set.length);
+  testLength(10, set);
 
   for (int i = 10; i < 20; i++) {
     Expect.isFalse(set.contains(i));
   }
 
   // Test Set.forEach.
   int sum = 0;
   testForEach(int val) {
     sum += (val + 1);
   }
@@ skipping 107 matching lines @@
     Expect.equals(i.isEven && (i % 3) != 0, difference.contains(i));
   }
   Expect.isTrue(twice.difference(thrice).difference(twice).isEmpty);
 
   // Test Set.addAll.
   List list = new List(10);
   for (int i = 0; i < 10; i++) {
     list[i] = i + 10;
   }
   set.addAll(list);
-  Expect.equals(20, set.length);
+  testLength(20, set);
   for (int i = 0; i < 20; i++) {
     Expect.isTrue(set.contains(i));
   }
 
   // Test Set.removeAll
   set.removeAll(list);
-  Expect.equals(10, set.length);
+  testLength(10, set);
   for (int i = 0; i < 10; i++) {
     Expect.isTrue(set.contains(i));
   }
   for (int i = 10; i < 20; i++) {
     Expect.isFalse(set.contains(i));
   }
 
   // Test Set.clear.
   set.clear();
-  Expect.equals(0, set.length);
+  testLength(0, set);
   set.add(11);
-  Expect.equals(1, set.length);
+  testLength(1, set);
+}
+
+void testLength(int length, Set set) {
+  Expect.equals(length, set.length);
+  (length == 0 ? Expect.isTrue : Expect.isFalse)(set.isEmpty);
+  (length != 0 ? Expect.isTrue : Expect.isFalse)(set.isNotEmpty);
 }
 
 main() {
   testMain(() => new Set());
   testMain(() => new HashSet());
 }