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https://github.com/ujihisa/rant

Ruby Imperative Random Data Generator and Quickcheck
https://github.com/ujihisa/rant

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Ruby Imperative Random Data Generator and Quickcheck

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h1. Imperative Random Data Generator and Quickcheck



You can use Rant to generate random test data, and use its Test::Unit extension for property-based testing.



Rant is basically a recursive descent interpreter, each of its method returns a random value of some type (string, integer, float, etc.).



Its implementation has no alien mathematics inside. Completely side-effect-free-free.



h1. Install





$ gem install hayeah-rant --source http://gems.github.com






$ irb

> gem 'rant'

> require 'rant'

> Rant.gen.value { [integer,float] }

=> [20991307, 0.025756845811823]

> Rant.gen.value { [integer,float]}

=> [-376856492, 0.452245765751706]




h1. Data Generation



You can create random generators from the Rant class. Rant.gen is just returns a class instance of Rant.





> gen = Rant.new

> gen.value { [integer,float] }

=> [-163260081, 0.356075765934108]




h2. Getting Random Data Values





Rant#each(n,limit=10)

  call a random block n times

Rant#map(n,limit=10)

  call the generator n times, and collect values

Rant#inject and other Enumerable methods

  ditto

Rant#value(limit=10)

  call a random block once, and get its value.




To collect an array of random data,





# we want 5

> gen.map(5) { integer }

=> [-380638946, -29645239, 344840868, 308052180, -154360970]




To iterate over random data,





> gen.each(5) { puts integer }

296971291

504994512

-402790444

113152364

502842783

=> nil




To get one value of random data,





> gen.value { integer }

=> 278101042




The optional argument @limit@ is used with generator guard. By default, if you want to generate n items, the generator tries at most n * 10 times.



This almost always succeeds,





> gen.map(5) { i = integer; guard i > 0; i }

=> [511765059, 250554234, 305947804, 127809156, 285960387]




This always fails,





> gen.map(10) { guard integer.is_a?(Float) }

Rant::TooManyTries: Exceed gen limit 100: 101 failed guards)




h2. Random Generating Methods



The API is similiar to QuickCheck, but not exactly the same. In particular @choose@ picks a random element from an array, and @range@ picks a integer from an interval.



h3. Simple Randomness





Rant#integer(n=nil)

  random positive or negative integer. Fixnum only.

Rant#range(lo,hi)

  random integer between lo and hi.

Rant#float

  random float

Rant#bool

  true or false

Rant#literal(value)

  No-op. returns value.

Rant#choose(*vals)

  Pick one value from among vals.




h3. Meta Randomness



A rant generator is just a mini interpreter. It's often useful to go meta,





Rant#call(gen)

  If gen is a Symbol, just do a method call with send.

  If gen is an Array, the first element of the array is the method name, the rest are args.

  If gen is a Proc, instance_eval it with the generator.






> gen.value { call(:integer) }

=> -240998958






> gen.value { call([:range,0,10]) }

=> 2






> gen.value { call(Proc.new { [integer] })}

=> [522807620]




The @call@ method is useful to implement other abstractions (See next subsection).





Rant#branch(*args)

  Pick a random arg among args, and Rant#call it.




50-50 chance getting an integer or float,





> gen.value { branch :integer, :float }

=> 0.0489446702931332

> gen.value { branch :integer, :float }

=> 494934533




h3. Frequencies





Rant#freq(*pairs)

  Takes a list of 2-tuples, the first of which is the weight, and the second a Rant#callable value, and returns a random value picked from the pairs. Follows the distribution pattern specified by the weights.




Twice as likely to get a float than integer. Never gets a ranged integer.





> gen.value { freq [1,:integer], [2,:float], [0,:range,0,10] }




If the "pair" is not an array, but just a symbol, @freq@ assumes that the weight is 1.





# 50-50 between integer and float

> gen.value { freq :integer, :float }




If a "pair" is an Array, but the first element is not an Integer, @freq@ assumes that it's a Rant method-call with arguments, and the weight is one.





# 50-50 chance generating integer limited by 10, or by 20.

> gen.value { freq [:integer,10], [:integer 20] }




h3. Sized Structure



A Rant generator keeps track of how large a datastructure it should generate with its @size@ attribute.





Rant#size

 returns the current size

Rant#sized(n,&block)

 sets the size for the duration of recursive call of block. Block is instance_eval with the generator.




Rant provides two methods that depends on the size





Rant#array(*branches)

  returns a sized array consisted of elements by Rant#calling random branches.

Rant#string(char_class=:print)

  returns a sized random string, consisted of only chars from a char_class.




The avaiable char classes for strings are:





:alnum

:alpha

:blank

:cntrl

:digit

:graph

:lower

:print

:punct

:space

:upper

:xdigit

:ascii






# sized 10 array of integer or float

> gen.value { sized(10) { array(:integer,:float)}}

=> [417733046, -375385433, 0.967812380000118, 26478621, 0.888588160450082, 250944144, 305584916, -151858342, 0.308123867823313, 0.316824642414253]



# fails if you forget to set the size.

> gen.value { array(:integer,:float)}

RuntimeError: size not set






If you set the size once, it applies to all subsequent recursive structures. Here's a sized 10 array of sized 10 strings,





> gen.value { sized(10) { array(:string)} }

=> ["1c}C/,9I#}", "hpA/UWPJ\\j", "H'~ERtI`|]", "%OUaW\\%uQZ", "Z2QdY=G~G!", "HojnxGDT3", "]a:L[B>bhb", "_Kl=&{tH^<", "ly]Yfb?`6c"]




Or a sized 10 array of sized 5 strings,





> gen.value { sized(10) { array Proc.new {sized(5) {string}}}}

=> ["S\"jf ", "d\\F-$", "-_8pa", "IN0iF", "SxRV$", ".{kQ7", "6>;fo", "}.D8)", "P(tS'", "y0v/v"]




Rant#array actually just delegate to Rant#freq, so you can use freq pairs:





> gen.value { sized(10) {array [1,:integer],[2,:float] }}

=> [0.983334733158678, -418176338, 0.976947175363592, 0.703390570421286, -478680395, 5483631, 0.966944106783513, 110469205, 0.540859146793544, 0.521813810037025]




h1. Property Testing



Rant extends Test::Unit for property testing. The extension is in its own module. So you need to require it.





require 'rant/check'




It defines,





Test::Unit::Assertions#property_of(&block)

  The block is used to generate random data with a generator. The method returns a Rant::Property instance, that has the method 'check'.




It's like this, using the gem 'shoulda'





# checks that integer only generates fixnum.

should "generate Fixnum only" do

   property_of  { integer }.check { |i| assert i.is_a?(Integer) }

end




The check block takes the generated data as its argument. One idiom I find useful is to include a parameter of the random data for the check argument. For example, if I want to check that Rant#array generates the right sized array, I could say,





should "generate right sized array" do

  property_of {

    len = integer

    [len,sized(len) { array :integer }]

  }.check { |(len,arr)|

    assert_equal len, arr.length

  }

end




That's about it. Enjoy :)



h1. Copyright



Copyright (c) 2009 Howard Yeh. See LICENSE for details.