HasSelfTests is found in core/selftest.py. You'll need to have ExternalSearchIndex subclass this class and implement the _run_self_tests method.

This method needs to yield a sequence of SelfTestResult objects – one for each distinct test we run. As we fill out this story, the number of tests we run will increase.

See the _run_self_tests implementation in api/overdrive.py for an example.

To start with, use the default search string to do a search against the search index, using ExternalSearchIndex.query_works. This will return a list of Work objects. The list of titles of the works will make a good value for the .result field of the SelfTestResult object.