Lint to prefer x.isNotEmpty vs. !x.isEmpty (#143).

test/rules/prefer_is_not_empty.dart

Index: test/rules/prefer_is_not_empty.dart
diff --git a/test/_data/p4/lib/lib1.dart b/test/rules/prefer_is_not_empty.dart
similarity index 51%
copy from test/_data/p4/lib/lib1.dart
copy to test/rules/prefer_is_not_empty.dart
index 083ff6fd68126469e314cff0d8f8bf7630173acb..155ed523f9b997b86288f3a3a5399acde86a3604 100644
--- a/test/_data/p4/lib/lib1.dart
+++ b/test/rules/prefer_is_not_empty.dart
@@ -2,12 +2,12 @@
 // 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 lib1;
+bool lne = ![].isEmpty; //LINT [12:11]
+bool mne = !{}.isEmpty; //LINT
+bool ine = !iterable.isEmpty; //LINT
 
-import 'package:p4/lib2.dart';
+bool le = [].isEmpty;
+bool me = {}.isEmpty;
+bool ie = iterable.isEmpty;
 
-import 'lib3.dart';
-
-void test() {
-  f(g());
-}
+Iterable get iterable => [];