README.markdown

# Welcome to Triq -- Trifork QuickCheck for Erlang

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Triq (pronounced "Trick Check") is a free alternative to [QuviQ
eqc](http://www.quviq.com/). Triq's API is modelled closely after
`eqc`, so I recommend their tutorials and slides for an introduction
to QuickCheck.  Notice that QuviQ `eqc` has many features not found in
`triq`, but it is open source licensed under the Apache license.  For
instance, `eqc` has features for reporting, management, probably a
much better shrinking mechanism, cool C integration, and
professional support.


## Installation

To use `triq`, you download the latest version from
[here](http://github.com/krestenkrab/triq/downloads), and untar it
into your erlang lib directory (typically
`/usr/local/lib/erlang/lib`):

```sh
prompt$ cd /usr/local/lib/erlang/lib
propmt$ tar xvzf triq-0.1.0.tgz
...
```

And you're all set.

Or, checkout the triq source code and soft link / copy into your Erlang lib directory:

```sh
prompt$ git clone git://github.com/krestenkrab/triq.git
prompt$ cd triq
prompt$ ln -s . /usr/local/lib/erlang/lib/triq-0.1.0
```

Next, to use `triq`, include the header file:

```erlang
-include_lib("triq/include/triq.hrl").
```

And you're ready to write property tests.  An example property could be:

```erlang
prop_append() ->
    ?FORALL({Xs,Ys},{list(int()),list(int())},
            lists:reverse(Xs++Ys)
            ==
            lists:reverse(Ys) ++ lists:reverse(Xs)).
```

To test this property, run `triq:check/1`, thus:

```erlang
1> triq:check(prop_append()).
......................................................................
..............................
Ran 100 tests
true
2>
```

If the test fails, it will try to shrink the result; here is an example:

```erlang
prop_delete() ->
    ?FORALL(L,list(int()),
        ?IMPLIES(L /= [],
            ?FORALL(I,elements(L),
                ?WHENFAIL(io:format("L=~p, I=~p~n", [L,I]),
                          not lists:member(I,lists:delete(I,L)))))).
```

Which runs like this:
```erlang
1> triq:check(triq_tests:prop_delete()).
x....Failed!
L=[4,5,5], I=5

Failed after 5 tests with false
Simplified:
        L = [0,0]
        I = 0
false
2>
```

You can get the values used for the failing test with `counterexample`,
and reuse the same test values with `check/2`:
```erlang
3> A = triq:counterexample(triq_tests:xprop_delete()).
x.xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxFailed!
L=[3,2,1,1,1], I=1

Failed after 101 tests with false
Simplified:
	L = [0,0]
	I = 0
[[0,0],0]
4> A.
[[0,0],0]
5> triq:check(triq_tests:xprop_delete(), A).
Failed!
L=[0,0], I=0

Failed after 1 tests with false
Simplified:
	L = [0,0]
	I = 0
false
6>
```

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.

```erlang
1> mymodule:check().
```

A handy addition that I use is to also add an `eunit` test, which tests it:

```erlang
property_test() -> true == check().
```
Which can then automatically be run using your favourite `eunit` runner.

Good luck!