The test for browsers is
a-element.html. The reusable format is
urltestdata.txt, which is not documented in detail. Reverse engineering through
urltestparser.js should not be too hard. Documentation welcome!
annevk/url hosts some other files that might be of interest if you want to create additional tests.
a-element.html it would be trivial to add more tests for other objects that expose links (e.g. URL and
<area>). There's also room for enhancement and bits that require independent tests: