testharness.jstestharness.js is a framework for writing low-level tests of browser functionality in javascript. It provides a convenient API for making assertions and is intended to work for both simple synchronous tests, and tests of asynchronous behaviour.
To use testharness.js you must include two scripts, in the order given:
<script src=/resources/testharness.js></script> <script src=/resources/testharnessreport.js></script>
For detailed API documentation please visit https://web-platform-tests.org/writing-tests/testharness-api.html.
You can also read a tutorial on Using testharness.js.