Adding isNotEmpty property to collection and string.

tests/corelib/string_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.
 
 import "package:expect/expect.dart";
 
 // TODO(ngeoffray): test String methods with null arguments.
 class StringTest {
 
   static testMain() {
     testOutOfRange();
     testIllegalArgument();
     testConcat();
     testIndex();
     testCodeUnitAt();
     testEquals();
     testEndsWith();
     testStartsWith();
     testIndexOf();
     testLastIndexOf();
     testContains();
     testReplaceAll();
     testCompareTo();
     testCharCodes();
   }
 
+  static void testLength() {
+    String str = "";
+    for (var i = 0; i < 20; i++) {
+      testStringLength(i, str);
+      str += " ";
+    }
+  }
+
   static void testOutOfRange() {
     String a = "Hello";
     bool exception_caught = false;
     try {
       var c = a[20];  // Throw exception.
     } on RangeError catch (e) {
       exception_caught = true;
     }
     Expect.equals(true, exception_caught);
   }
 
   static testIllegalArgument() {
     String a = "Hello";
     bool exception_caught = false;
     try {
       var c = a[2.2];  // Throw exception.
       Expect.equals(true, false);
     } on ArgumentError catch (e) {
       exception_caught = true;
     } on TypeError catch (e) {  // Thrown in checked mode only.
       exception_caught = true;
     }
     Expect.equals(true, exception_caught);
   }
 
   static testIndex() {
     String str = "string";
     for (int i = 0; i < str.length; i++) {
       Expect.equals(true, str[i] is String);
-      Expect.equals(1, str[i].length);
+      testStringLength(1, str[i]);
     }
   }
 
   static testCodeUnitAt() {
     String str = "string";
     for (int i = 0; i < str.length; i++) {
       Expect.equals(true, str.codeUnitAt(i) is int);
     }
   }
 
   static testConcat() {
     var a = "One";
     var b = "Four";
     var c = a + b;
-    Expect.equals(7, c.length);
+    testStringLength(7, c);
     Expect.equals("OneFour", c);
   }
 
   static testEquals() {
     Expect.equals("str", "str");
 
     Expect.equals("str", "s" + "t" + "r");
     Expect.equals("s" + "t" + "r", "str");
 
     Expect.equals(false, "str" == "s");
@@ skipping 197 matching lines @@
       for (int i = 0; i < str.length; i++) {
         Expect.equals(str.codeUnitAt(i), list[i]);
       }
     }
     test("abc");
     test("");
     test(" ");
   }
 }
 
+void testStringLength(int length, String str) {
+  Expect.equals(length, str.length);
+  (length == 0 ? Expect.isTrue : Expect.isFalse)(str.isEmpty);
+  (length != 0 ? Expect.isTrue : Expect.isFalse)(str.isNotEmpty);
+}
+
 main() {
   StringTest.testMain();
 }