Test documents have a suffix of .json, like basic.json.

Selectors to be applied to test documents have the document name, followed by an underbar, followed by a description of the test, with a .selector file name suffix, like basic_grouping.selector.

Expected output files have the same name as the .selector file, but have a .output suffix, like basic_grouping.output.

Expected output files contain a stream of JSON objects that are what is expected to be produced when a given selector is applied to a given document.