Add isNotEmpty to core_matchers.

pkg/matcher/lib/src/core_matchers.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.
 
 library matcher.core_matchers;
 
 import 'description.dart';
 import 'interfaces.dart';
 import 'util.dart';
 
 /// Returns a matcher that matches empty strings, maps or iterables
-/// (including collections).
+/// (including collections) using the isEmpty property.
 const Matcher isEmpty = const _Empty();
 
 class _Empty extends Matcher {
   const _Empty();
   bool matches(item, Map matchState) {
-    if (item is Map || item is Iterable) {
-      return item.isEmpty;
-    } else if (item is String) {
-      return item.length == 0;
-    } else {
-      return false;
-    }
+    return (item is Map || item is Iterable || item is String) && item.isEmpty;
   }
   Description describe(Description description) => description.add('empty');
 }
 
+/// Returns a matcher that matches non-empty strings, maps or iterables
+/// (including collections) using the isNotEmpty property.
+const Matcher isNotEmpty = const _NotEmpty();
+
+class _NotEmpty extends Matcher {
+  const _NotEmpty();
+
+  bool matches(item, Map matchState) {
+    return (item is Map || item is Iterable || item is String) &&
+      item.isNotEmpty;
+  }
+  
+  Description describe(Description description) => description.add('non-empty');
+}
+
 /// A matcher that matches any null value.
 const Matcher isNull = const _IsNull();
 
 /// A matcher that matches any non-null value.
 const Matcher isNotNull = const _IsNotNull();
 
 class _IsNull extends Matcher {
   const _IsNull();
   bool matches(item, Map matchState) => item == null;
   Description describe(Description description) => description.add('null');
@@ skipping 600 matching lines @@
         addDescriptionOf(matchState['feature']);
     var innerDescription = new StringDescription();
     _matcher.describeMismatch(matchState['feature'], innerDescription,
         matchState['state'], verbose);
     if (innerDescription.length > 0) {
       mismatchDescription.add(' which ').add(innerDescription.toString());
     }
     return mismatchDescription;
   }
 }