Add support for specifying SDK version constraints in pubspecs.

utils/tests/pub/version_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 version_test;
 
 import '../../../pkg/unittest/lib/unittest.dart';
+import 'test_pub.dart';
 import '../../pub/utils.dart';
 import '../../pub/version.dart';
 
 main() {
   final v123 = new Version.parse('1.2.3');
   final v114 = new Version.parse('1.1.4');
   final v124 = new Version.parse('1.2.4');
   final v200 = new Version.parse('2.0.0');
   final v234 = new Version.parse('2.3.4');
   final v250 = new Version.parse('2.5.0');
@@ skipping 277 matching lines @@
       });
     });
 
     test('isEmpty', () {
       expect(new VersionRange().isEmpty, isFalse);
       expect(new VersionRange(min: v123, max: v124).isEmpty, isFalse);
     });
   });
 
   group('VersionConstraint', () {
+    test('any', () {
+      expect(VersionConstraint.any.isAny, isTrue);
+      expect(VersionConstraint.any, allows([
+        new Version.parse('0.0.0-blah'),
+        new Version.parse('1.2.3'),
+        new Version.parse('12345.678.90')]));
+    });
+
     test('empty', () {
-      expect(new VersionConstraint.empty().isEmpty, isTrue);
+      expect(VersionConstraint.empty.isEmpty, isTrue);
+      expect(VersionConstraint.empty, doesNotAllow([
+        new Version.parse('0.0.0-blah'),
+        new Version.parse('1.2.3'),
+        new Version.parse('12345.678.90')]));
     });
 
     group('parse()', () {
       test('parses an exact version', () {
         var constraint = new VersionConstraint.parse('1.2.3-alpha');
         expect(constraint is Version, isTrue);
         expect(constraint, equals(new Version(1, 2, 3, pre: 'alpha')));
       });
 
       test('parses "any"', () {
@@ skipping 109 matching lines @@
 
 Matcher allows(List<Version> versions) =>
     new VersionConstraintMatcher(versions, true);
 
 Matcher doesNotAllow(List<Version> versions) =>
     new VersionConstraintMatcher(versions, false);
 
 throwsIllegalArg(function) {
   expect(function, throwsA((e) => e is ArgumentError));
 }