Adding isNotEmpty property to collection and string.

tests/corelib/string_buffer_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(srdjan): Move StringBuffer to visible names.
 
 void testConstructor() {
   StringBuffer bf = new StringBuffer("");
-  Expect.equals(true, bf.isEmpty);
+  testBufferLength(0, bf);
 
   bf = new StringBuffer("abc");
-  Expect.equals(3, bf.length);
+  testBufferLength(3, bf);
   Expect.equals("abc", bf.toString());
 
   bf = new StringBuffer("\x00");
 }
 
 void testWrite() {
   StringBuffer bf = new StringBuffer("");
   Expect.equals(true, bf.isEmpty);
 
   bf.write("a");
-  Expect.equals(1, bf.length);
+  testBufferLength(1, bf);
   Expect.equals("a", bf.toString());
 
   bf = new StringBuffer("");
   bf.write("a");
   bf.write("b");
   Expect.equals("ab", bf.toString());
 
   bf = new StringBuffer("abc");
   bf.write("d");
   bf.write("e");
@@ skipping 27 matching lines @@
   bf = new StringBuffer("");
   for (int i = 0; i < 100000; i++) {
     bf.write('');
     bf.write("");
   }
   Expect.equals("", bf.toString());
 }
 
 void testLength() {
   StringBuffer bf = new StringBuffer("");
-  Expect.equals(0, bf.length);
+  testBufferLength(0, bf);
   bf.write("foo");
-  Expect.equals(3, bf.length);
+  testBufferLength(3, bf);
   bf.write("bar");
-  Expect.equals(6, bf.length);
+  testBufferLength(6, bf);
   bf.write("");
-  Expect.equals(6, bf.length);
+  testBufferLength(6, bf);
 }
 
 void testIsEmpty() {
   StringBuffer bf = new StringBuffer("");
   Expect.equals(true, bf.isEmpty);
   bf.write("foo");
   Expect.equals(false, bf.isEmpty);
 }
 
 void testWriteAll() {
   StringBuffer bf = new StringBuffer("");
   bf.writeAll(["foo", "bar", "a", "b", "c"]);
   Expect.equals("foobarabc", bf.toString());
 
   bf.writeAll([]);
   Expect.equals("foobarabc", bf.toString());
 
   bf.writeAll(["", "", ""]);
   Expect.equals("foobarabc", bf.toString());
 }
 
 void testClear() {
   StringBuffer bf = new StringBuffer("");
   bf.write("foo");
   bf.clear();
   Expect.equals("", bf.toString());
-  Expect.equals(0, bf.length);
+  testBufferLength(0, bf);
 
   bf.write("bar");
   Expect.equals("bar", bf.toString());
-  Expect.equals(3, bf.length);
+  testBufferLength(3, bf);
   bf.clear();
   Expect.equals("", bf.toString());
-  Expect.equals(0, bf.length);
+  testBufferLength(0, bf);
 }
 
 void testToString() {
   StringBuffer bf = new StringBuffer("");
   Expect.equals("", bf.toString());
 
   bf = new StringBuffer("foo");
   Expect.equals("foo", bf.toString());
 
   bf = new StringBuffer("foo");
@@ skipping 41 matching lines @@
   bf1.writeCharCode(0x63);
   bf1.write("d");
   bf1.writeCharCode(0x65);
   Expect.equals("abcdeabcde", bf1.toString());
 
   // Out-of-range character codes are not allowed.
   Expect.throws(() { bf2.writeCharCode(-1); });
   Expect.throws(() { bf2.writeCharCode(0x110000); });
 }
 
+void testBufferLength(int length, StringBuffer bf) {
+  Expect.equals(length, bf.length);
+  (length == 0 ? Expect.isTrue : Expect.isFalse)(bf.isEmpty);
+  (length != 0 ? Expect.isTrue : Expect.isFalse)(bf.isNotEmpty);
+}
+
 void main() {
   testToString();
   testConstructor();
   testLength();
   testIsEmpty();
   testWrite();
   testWriteCharCode();
   testWriteAll();
   testClear();
   testChaining();
 }