#+OPTIONS: ^:nil
#+TITLE: Triq

* [[][Triq]] QuickCheck for Erlang

** Introduction
   :CUSTOM_ID: introduction

Triq (Term Reductive Invariant Questant) is an Apache licensed
QuickCheck library for Erlang. It is a continuation and community fork
of [[][Trifork QuickCheck]]. Unlike the original project, this fork is in
*no way* affiliated with or a product of Trifork.

By and large, the Triq API is modeled closely after QuviQ =eqc=,
except you want to replace any occurrence of =eqc= with =triq=. The
main supporting module is called =triq_dom=, corresponding to eqc's

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** Writing QuickCheck properties with Triq
    :CUSTOM_ID: writing-properties-with-triq

To write properties with =triq=, include the =triq.hrl= header file:


Modules compiled with the =triq.hrl= header auto-export all functions
named =prop_*=, and have a function added called =check/0= which runs
=triq:check/1= on all the properties in the module. Further, adding
the attribute =-triq(eunit)= will generate EUnit tests for all
properties, turning the module into a regular EUnit test suite.

If you use, you will typically want to use [[][the built-in Triq
plugin]] to check properties. Otherwise we highly recommend letting Triq
generate EUnit tests, thus arriving at a demo module like this:

prop_append() ->
            lists:reverse(Ys) ++ lists:reverse(Xs)).

Now, all you have to do is run =rebar3 eunit=:

$ rebar3 eunit -v
===> Verifying dependencies...
===> Compiling triq_demo
===> Performing EUnit tests...
======================== EUnit ========================
file ""
  application 'triq_demo'
    triq_demo:5: append_test_ (module 'triq_demo')...[0.262 s] ok
    [done in 0.269 s]
  [done in 0.274 s]
  Test passed.

If you use =-triq({eunit, [{runs, N}]})=, then Triq will do =N= runs for each
property in the module, which is equivalent to calling =triq:check(Module, N)=.
This can be useful to make Triq try more (or less) cases than the default.

For advanced features, please consult the API docs.

** Obtaining Triq
   :CUSTOM_ID: obtaining-triq

*** Installation via package manager
    :CUSTOM_ID: installation-via-package-manager

To use =triq=, you can add it as a project dependency and let your
package manager of choice handle it:

| rebar.config | ={deps, [triq]}=    |
|    | =DEPS = triq=       |
| mix.exs      | ={:triq, "~> 1.*"}= |

*** Installation from source into =$ERL_LIBS=
    :CUSTOM_ID: installation-from-source-into-erl_libs

If you want to make =triq= available globally, you can install it from
source into your Erlang installation by adding it in one of your
=$ERL_LIBS= paths. So, it's either somewhere like
=/usr/lib/erlang/lib= or =$HOME/.erl=.

You can either download a [[][tagged release]]
and extract that or clone the [[][git repo]] in the
target directory. Once that's done, cd into the directory and run =make=.

Now, if you start =erl=, you should be able to call functions from the
=triq= module.

    $ erl
    1> code:which(triq).