Add isNotEmpty to core_matchers.

pkg/matcher/test/iterable_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.iterable_matchers_test;
 
 import 'package:matcher/matcher.dart';
 import 'package:unittest/unittest.dart' show test, group;
 
 import 'test_utils.dart';
 
 void main() {
   initUtils();
 
   test('isEmpty', () {
     shouldPass([], isEmpty);
     shouldFail([1], isEmpty, "Expected: empty Actual: [1]");
   });
 
+  test('isNotEmpty', () {
+    shouldFail([], isNotEmpty, "Expected: non-empty Actual: []");
+    shouldPass([1], isNotEmpty);
+  });
+
   test('contains', () {
     var d = [1, 2];
     shouldPass(d, contains(1));
     shouldFail(d, contains(0), "Expected: contains <0> "
         "Actual: [1, 2]");
   });
 
   test('equals with matcher element', () {
     var d = ['foo', 'bar'];
     shouldPass(d, equals(['foo', startsWith('ba')]));
@@ skipping 127 matching lines @@
         "Expected: pairwise less than [1, 4, 9] "
         "Actual: [1, 2, 3] "
         "Which: has <1> which is not less than <1> at index 0");
     shouldPass(d, pairwiseCompare(e, (e,a) => a * a == e, "square root of"));
     shouldFail(d, pairwiseCompare(e, (e,a) => a + a == e, "double"),
         "Expected: pairwise double [1, 4, 9] "
         "Actual: [1, 2, 3] "
         "Which: has <1> which is not double <1> at index 0");
   });
 }