Created: 2008-11-21 19:42
Updated: 2018-06-02 17:55



etap is a collection of Erlang modules that provide a TAP testing client library. These modules allow developers to create extensive and comprehensive tests covering many aspects of application and module development. This includes simple assertions, exceptions, the application behavior and event web requests. This library was originally written by Jeremy wall.

As per the TAP wiki:

TAP, the Test Anything Protocol, is a simple text-based interface between testing modules in a test harness. TAP started life as part of the test harness for Perl but now has implementations in C/C++, Python, PHP, Perl and probably others by the time you read this.

These modules are not meant to compete with eunit, but to offer a more general testing facility that isn't provided by eunit.


A "test" is any number of etap:* or etap_*:* tests that are part of a test plan. When a plan is created using etap:plan/1, a process is started that tracks the status of the tests executed and handles diagnostic output.

Consider the following example test plan:

etap:ok(true, "the 'true' atom is recognized"),
etap:is(1 + 1, 2, "simple math"),
etap:isnt(2 + 2, 5, "some would argue"),

For tests that require pattern matching, a macro can be used.

?ETAP_MATCH({foo, bar, baz}, {foo, _, _}, "a three-element tuple with foo as the first element"),

There are a number of utility tests that can be used. The etap:any/3, etap:none/3, etap:fun_is/3, and etap:expect_fun/3 use functions to return either 'true' or 'false'.

Numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9],
FunWithNumbers = fun(X) case X of [1, 2, 3 | _] -> true; _ -> false end end,
etap:fun_is(FunWithNumbers, Numbers, "Match the first three numbers").

There are many examples in t/*.erl.


To build this library, from the root directory execute the make command. You should also execute the make test command to verify that the library functions correctly on your system. If you have the Perl module TAP::Harness you can use it to collect and display test results using the make prove target.

$ make
$ make test
$ make prove

If you choose to run the make test command then please be sure to make clean after to remove any of the temporary beam files created by the tests in the t/ directory.

The included tests cover the basic functionality of the etap modules. They can also be used as a reference when writing your own tests.

To install etap you need to create the etap/ebin/ directory in your current Erlang library and copy all of the .beam files created by the make file.

$ sudo mkdir -p /usr/lib/erlang/lib/etap-0.3.4/ebin
$ make clean && make
$ sudo cp ebin/*.beam /usr/lib/erlang/lib/etap-0.3.4/ebin/

The make dist-src target can be used to create source distributions for further packaging and deployment.

USING TAP::Harness

The 'TAP::Harness' library can be used to collect TAP output produced by this module.

$ cpan install TAP::Harness
$ prove t/*.t
$ prove -v t/*.t


With etap it is possible to test the code coverage of your test suite. To enable code coverage you must set the "COVER" environmental variable and post-compile all of the .coverdata files created by the test suite.

$ COVER=1 erl -eval 'module:test().' -s init stop ...
$ COVER=1 escript t/*.t
$ COVER=1 prove t/*.t
$ erl
1> etap_report:create().

There are several assumptions made here:

  • All of the modules you are trying to get coverage for reside in the ./ebin/ directory. If this is not the case, the directory can be set using the "COVER_BIN" environmental variable.
  • All of the .beam files analyzed by this code coverage feature are compiled with the +debug_info flag.


There are a number of proposals listed on the TAP wiki that are not supported by this library. Please be aware of this when creating your tests.

  • LIMITED SUPPORTED: TAP diagnostic syntax
  • LIMITED SUPPORTED: TAP meta information
  • LIMITED SUPPORTED: TAP logging syntax
  • SUPPORTED: TAP datetime
  • SUPPORTED: c0 code coverage
  • SUPPORTED: html code coverage reports

We Need Your Help!

Things that can greatly be improved. Please fork this project and contribute. Patches are always welcome.

  • Support for testing multi-node systems and environments.
  • OTP behaviors like gen_server, gen_fsm and gen_event
  • Things like the error_logger and sasl
  • C1 code coverage reporting and html output
  • Documentation

I've got a project. How can I integrate testing?

If you haven't been a test-first developer before, now is the best time to start. To integrate etap into your project, you need to do 3 things.

  1. Install etap onto your development/build/integration system.
  2. Create tests! Start with really simple things like loading modules and gradually build tests into more and more complex and deep functionality.
  3. Run your tests. This is the most important step. Get into the habit of running your test suite before every check-in, after every pull, before packaging, etc.


2008-2009 Nick Gerakines
2007-2008 Jeremy Wall
2008 Jacob Vorreuter

Special thanks to everyone that has contributed to this project.

  • Paul J. Davis
  • Brad Anderson
  • Ken Pratt
  • Kevin Ilchmann Jørgensen
  • Benoit Chesneau
  • Adam Kocoloski
  • Jayson Vantuyl
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