Fantasy Check

General

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

   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:

   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!",
   )

Laws

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

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

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

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

Testing

Library

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.

Coverage

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.