This adds a unit test to show the type checking functionality missing in dartc

tests/language/src/TypeChecksInFactoryMethodTest.dart

+// Copyright (c) 2011, 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.
+// VMOptions=--enable_type_checks --enable_asserts
+// Tests the type checking when passing code into closure from inside a factory method
+
+interface Foo<T> default Bar {
+  Foo.from();
+}
+
+class Bar<T> implements Foo<T> {
+  Bar() {}
+
+  factory Bar.from() {
+    var func = (T arg) { T foo = arg; print(arg); }; 
+    // If T is not a string, runtime type checks should fail

[codefu, 2011/12/22 16:13:50]

And instance-of check should also fail.

+    func("Hello World!");
+    return new Bar<T>();
+  }
+}
+
+main() {
+  Foo value;
+  value = new Foo<String>.from();
+
+  bool gotError = false;
+
+  try {
+    value = new Foo<int>.from();
+  } catch (TypeError e) {
+    gotError = true;
+  }
+  Expect.equals(true, gotError);
+}