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Bisect_ppx   version 1.3.4 Travis status Coverage

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.

Bisect_ppx usage example

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, OASIS and Jbuilder.

     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!

    In each file of the report,

    • Green lines contain expressions, all of which were visited.
    • Red lines contain expressions, none of which were visited.
    • Yellow lines contain expressions, some of which were visited, but others not.
    • White lines are those that don't contain visitable expressions. They may have type declarations, keywords, or something else that Bisect_ppx did not, or cannot instrument.

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.

Bisect_ppx in practice

A small sample of projects using Bisect_ppx:


Bisect_ppx is available under the Mozilla Public License 2.0 (MPL). To summarize, you can incorporate Bisect_ppx into proprietary projects. If you make modifications to Bisect_ppx, you have to open-source them. The rest of your project remains proprietary.

Essentially, this is like the BSD or MIT licenses, except that if you include a customized Bisect_ppx in a release (as opposed to private use), you have to make the altered source visible. This can be done by contributing the changes back, keeping Bisect_ppx in a visible fork, or if your bigger project itself also happens to be open source.

Besides proprietary licenses, MPL is compatible with BSD/MIT/Apache- and (L)GPL-licensed projects. See the MPL 2.0 FAQ.

The Ocamlbuild plugin is dedicated to the public domain.


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.