The organization of tests is the following:

- internal.ml contains the tests that should be runnable from a bare
  OCaml installation -- always passing the -no-ocamlfind option.

- findlibonly.ml contains the tests that should be runnable from a bare
  OCaml installation, with only ocamlfind/findlib on top. The only
  ocamlfind packages it relies over are those of the OCaml
  distribution.

- external.ml contains the tests that rely on other findlib packages
  or external tools to run. Each test will only run if the findlib
  package it depends on is present.