testharness.js subresources use testharnessreport.js `fetch_tests_from_window` will aggregate tests from separate windows or iframes into the current document as if they were all part of the same test suite. The document of the second window (or iframe) should include `testharness.js`, but not `testharnessreport.js`, and use `test`, `async_test`, and `promise_test` in the usual manner.