Add isNotEmpty to core_matchers.

pkg/matcher/test/core_matchers_test.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_test;
 
 import 'package:matcher/matcher.dart';
 import 'package:unittest/unittest.dart' show test, group;
 
 import 'test_utils.dart';
@@ skipping 75 matching lines @@
   test('returnsNormally', () {
     shouldPass(doesNotThrow, returnsNormally);
     shouldFail(doesThrow, returnsNormally,
         matches(
             r"Expected: return normally"
             r"  Actual: <Closure(: \(\) => dynamic "
             r"from Function 'doesThrow': static\.)?>"
             r"   Which: threw 'X'"));
   });
 
-
   test('hasLength', () {
     var a = new Map();
     var b = new List();
     shouldPass(a, hasLength(0));
     shouldPass(b, hasLength(0));
     shouldPass('a', hasLength(1));
     shouldFail(0, hasLength(0), new PrefixMatcher(
         "Expected: an object with length of <0> "
         "Actual: <0> "
         "Which: has no length property"));
@@ skipping 64 matching lines @@
   });
 
   group('Predicate Matchers', () {
     test('isInstanceOf', () {
       shouldFail(0, predicate((x) => x is String, "an instance of String"),
           "Expected: an instance of String Actual: <0>");
       shouldPass('cow', predicate((x) => x is String, "an instance of String"));
     });
   });
 }