In VSTS 2005, users can only add request-level validation rules from Web Test Editor; while in Orcas, Web Tests have a new collection of test-level validation rules. These rules will fire on every request in the test and are a shortcut for adding the same rule to every request. By default, rules will only apply to top-level requests.
A Test-level validation rule can be added by right clicking on the root node of a Web test and selecting “Add Validation Rule…” All test-level validation rules are listed under Validation Rules node in the Editor. After running a Web test, the results will be reported as if the rule were on the request.