First pass at version constraint solver.

utils/tests/pub/pubspec_test.dart

Index: utils/tests/pub/pubspec_test.dart
diff --git a/utils/tests/pub/pubspec_test.dart b/utils/tests/pub/pubspec_test.dart
index ba0a04ce0204ab197e120db17ce96fecc12b2e21..5ab53ddabf45f0d56f72697ea6d2d328234b9d1f 100644
--- a/utils/tests/pub/pubspec_test.dart
+++ b/utils/tests/pub/pubspec_test.dart
@@ -9,6 +9,7 @@
 #import('../../pub/source.dart');
 #import('../../pub/source_registry.dart');
 #import('../../pub/utils.dart');
+#import('../../pub/version.dart');
 
 class MockSource extends Source {
   final String name = "mock";
@@ -21,6 +22,24 @@ class MockSource extends Source {
 main() {
   group('Pubspec', () {
     group('parse()', () {
+      test("allows a version constraint for dependencies", () {
+        var sources = new SourceRegistry();
+        sources.register(new MockSource());
+
+        var pubspec = new Pubspec.parse('''
+dependencies:
+  foo:
+    mock: ok
+    version: ">=1.2.3 <3.4.5"
+''', sources);
+
+        var foo = pubspec.dependencies[0];
+        expect(foo.name, equals('foo'));
+        expect(foo.version.allows(new Version(1, 2, 3)));
+        expect(foo.version.allows(new Version(1, 2, 5)));
+        expect(!foo.version.allows(new Version(3, 4, 5)));
+      });
+
       test("throws if the description isn't valid", () {
         var sources = new SourceRegistry();
         sources.register(new MockSource());