testharness.js is a framework for writing low-level tests of
making assertions and is intended to work for both simple synchronous
tests, and tests of asynchronous behaviour.
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.