Fantasy Check



General

QuickCheck is a form of automated specification testing. Instead
of manually writing tests cases like so:

``javascript
assert(0 + 1 == 1);
assert(1 + 1 == 2);
assert(3 + 3 == 6);
`

We can just write the assertion algebraically and tell QuickCheck to
automatically generate lots of inputs:

`javascript
λ.forAll(
function(n) {
return n + n == 2 * n;
},
[Number]
).fold(
function(fail) {
return "Failed after " + fail.tries + " tries: " + fail.inputs.toString();
},
"All tests passed!",
)
`

$3

Fantasy Check allows the easy testing of various laws whilst being
unit testing framework agnostic.

* Functors
* Applicative Functors
* Monads
* More to follow...

Assuming you're using Fantasy Identities
and a adapter from the adapters package with the unit
testing framework.

#### Functors

The functor check has 2 different laws which allow you to test the
mapping of tagged types. Note - it should be possible to test
functions as well, by providing a map (aka compose) for the function
type.

* Identity
* Composition

`javascript
exports.law1 = functor.identity(λ)(Identity.of);
exports.law2 = functor.composition(λ)(Identity.of);
`

#### Applicative Functors

The applicative functor check has 4 different laws which allow you
to test:

* Identity
* Composition
* Homomorphism
* Interchange

`javascript
exports.law1 = functor.identity(λ)(Identity);
exports.law2 = functor.composition(λ)(Identity);
exports.law3 = functor.homomorphism(λ)(Identity);
exports.law4 = functor.interchange(λ)(Identity);
`

#### Monads

The monad check has 3 different laws which allow you
to test:

* Left Identity
* Right Identity
* Associativity

`javascript
exports.law1 = functor.leftIdentity(λ)(Identity);
exports.law2 = functor.rightIdentity(λ)(Identity);
exports.law3 = functor.associativity(λ)(Identity);
`

Testing

$3

Fantasy Check uses nodeunit for
all the tests and because of this there is currently an existing
adapter in the library to help with integration
between nodeunit and Fantasy Check.

$3

Currently Fantasy Check is using Istanbul
for code coverage analysis; you can run the coverage via the following
command:

_This assumes that you have istanbul installed correctly._

`
istanbul cover nodeunit -- test/*.js
``

It should report that the total coverage is at 100% for the whole lib.