The headers of a test are not just there for decoration; three properties are enforced when a test, say, (*$X foo is compiled, where X is T, R, Q,... :
Those two conditions put together offer a strong guarantee that, if a function is referenced in a test header, then it is actually tested at least once. The list of functions referenced in the headers of extracted tests is written by qtest into qtest.targets.log. Each line is of the form
foo.ml 42 foo
where foo.ml is the file in which the test appears, as passed to extract, and 42 is the line number where the test pragma appears in foo.ml. Note that a same function can be listed several times for the same source file, if several tests involve it (say, two times if it has both a simple test and a random one). The exact number of statements involving foo in each test is currently not taken into account in the logs.