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.
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]
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]
Getting Random Data Values
Rant#map(n,limit=10)
call the generator n times, and collect values
Rant#each(n,limit=10)
call a random block n times
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)
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.
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.
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
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] }
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(size=default_size)
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 { array(10) { branch(:integer,:float)}}
=> [417733046, -375385433, 0.967812380000118, 26478621, 0.888588160450082, 250944144, 305584916, -151858342, 0.308123867823313, 0.316824642414253]
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!", "H<o|<FARGQ", "g>ojnxGDT3", "]a:L[B>bhb", "_Kl=&{tH^<", "ly]Yfb?`6c"]
Or a sized 10 array of sized 5 strings,
> gen.value { array(10) { array(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]
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,array(len){integer}]
}.check { |(len,arr)|
assert_equal len, arr.length
}
end
That’s about it. Enjoy :)
Copyright
Copyright © 2009 Howard Yeh. See LICENSE for details.
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