Bisect_ppx is a code coverage tool for OCaml. It helps you test thoroughly by showing which parts of your code are not tested. You can also use it for tracing: run one test, and see what is visited.

For a live demonstration, see the coverage report Bisect_ppx generates for itself. You may also want to see projects that use Bisect_ppx.

Most of these commands go in a Makefile or other script, so that you only have to run that script, then refresh your browser.

1. Install Bisect_ppx.

    opam install bisect_ppx
   

   You can also install without OPAM.

2. When compiling for testing, include Bisect_ppx. Instructions are also available for Ocamlbuild and for OASIS.

    ocamlfind c -package bisect_ppx -c my_code.ml
    ocamlfind c -c my_tests.ml
    ocamlfind c -linkpkg -package bisect_ppx my_code.cmo my_tests.cmo
   

3. Run your test binary. In addition to testing your code, it will produce one or more files with names like bisect0001.out.

    ./a.out             # Produces bisect0001.out
   

4. Generate the coverage report.

    bisect-ppx-report -I build/ -html coverage/ bisect*.out`
   

5. Open coverage/index.html!

You can submit a coverage report to Coveralls.io using ocveralls. Note that Bisect_ppx reports are more precise than Coveralls, which only considers whole lines as visited or not.

See also the advanced usage.

A small sample of projects using Bisect_ppx:

• Oml: report
• ctypes: report
• ocaml-irc-client: report
• Markup.ml: report
• Ketrew
• Sosa

Bisect_ppx is an advanced fork of the excellent Bisect by Xavier Clerc. As of the time of this writing, it appears that the original Bisect is no longer maintained.

Considerable work has been done on Bisect_ppx, so that it is now a distinct project. In terms of the interface, Bisect_ppx is still largely compatible with Bisect's ppx mode, but see here for a list of differences.

If you use Camlp4, you will want to use the original Bisect.

Bisect_ppx is distributed under the terms of the GPL license, version 3. Note, however, that Bisect_ppx does not "contaminate" your project with the terms of the GPL, because it is a development tool used only during testing. You would not want to link Bisect_ppx into your release files anyway, for performance reasons.

Bug reports and pull requests are warmly welcome. Bisect_ppx is developed on GitHub, so please open an issue.

To get the latest development version of Bisect_ppx using OPAM, run

opam source --dev-repo --pin bisect_ppx

You will now have a bisect_ppx subdirectory to work in.