Path: | README.md |
Last Update: | Sat Dec 22 00:08:34 +0000 2018 |
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# Imperative Random Data Generator and Quickcheck
You can use Rantly to generate random test data, and use its Test::Unit extension for property-based testing.
Rantly 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
```ruby $ gem install rantly ```
```ruby $ irb -rrantly > Rantly { [integer,float] } # same as Rantly.value { integer }
> Rantly { [integer,float]}
> Rantly(5) { integer } # same as Rantly.map(5) { integer }
```
# Data Generation
## Getting Random Data Values
```ruby Rantly#map(n,limit=10,&block)
call the generator n times, and collect values
Rantly#each(n,limit=10,&block)
call a random block n times
Rantly#value(limit=10,&block)
call a random block once, and get its value.
```
To collect an array of random data,
```ruby # we want 5 random integers > Rantly(5) { integer }
```
To iterate over random data,
```ruby > Rantly.each(5) { puts integer } 296971291 504994512 -402790444 113152364 502842783
```
To get one value of random data,
```ruby > Rantly { integer }
```
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,
```ruby > Rantly(5) { i = integer; guard i > 0; i }
```
This always fails,
```ruby > Rantly(10) { guard integer.is_a?(Float) } Rantly::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
```ruby Rantly#integer(n=nil)
random positive or negative integer. Fixnum only.
Rantly#range(lo,hi)
random integer between lo and hi.
random float
true or false
No-op. returns value.
Pick one value from among vals.
```
## Meta Randomness
A rant generator is just a mini interpreter. It‘s often useful to go meta,
```ruby Rantly#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.
```
```ruby > Rantly { call(:integer) }
```
```ruby > Rantly { call([:range,0,10]) }
```
```ruby > Rantly { call(Proc.new { [integer] })}
```
The `call` method is useful to implement other abstractions (See next subsection).
```ruby Rantly#branch(*args)
Pick a random arg among args, and Rantly#call it.
```
50-50 chance getting an integer or float,
```ruby > Rantly { branch :integer, :float }
> Rantly { branch :integer, :float }
```
## Frequencies
```ruby Rantly#freq(*pairs)
Takes a list of 2-tuples, the first of which is the weight, and the second a Rantly#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.
```ruby > Rantly { 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.
```ruby # 50-50 between integer and float > Rantly { freq :integer, :float } ```
If a "pair" is an Array, but the first element is not an Integer, `freq` assumes that it‘s a Rantly method-call with arguments, and the weight is one.
```ruby # 50-50 chance generating integer limited by 10, or by 20. > Rantly { freq [:integer,10], [:integer 20] } ```
## Sized Structure
A Rantly generator keeps track of how large a datastructure it should generate with its `size` attribute.
```ruby Rantly#size
returns the current size
Rantly#sized(n,&block)
sets the size for the duration of recursive call of block. Block is instance_eval with the generator.
```
Rantly provides two methods that depends on the size
```ruby Rantly#array(size=default_size,&block)
returns a sized array consisted of elements by Rantly#calling random branches.
Rantly#string(char_class=:print)
returns a sized random string, consisted of only chars from a char_class.
Rantly#dict(size=default_size,&block)
returns a sized random hash. The generator block should generate tuples of keys and values (arrays that have two elements, the first one is used as key, and the second as value).
```
The avaiable char classes for strings are:
```ruby :alnum :alpha :blank :cntrl :digit :graph :lower :print :punct :space :upper :xdigit :ascii ```
```ruby # sized 10 array of integers > Rantly { array(10) { integer }}
```
If you set the size once, it applies to all subsequent recursive structures. Here‘s a sized 10 array of sized 10 strings,
```ruby > Rantly { sized(10) { array {string}} }
```
Or a sized 10 array of sized 5 strings,
```ruby > Rantly {array(10){sized(5) {string}}}
```
Generate a hash that has 5 elements,
```ruby > Rantly { dict { [string,integer] }} {"bR\qHn"=>247003509502595457,
"-Mp '."=>653206579583741142, "gY%<SV"=>-888111605212388599, "+SMn:r"=>-1159506450084197716, "^3gYfQ"=>-2154064981943219558, "= :/\\,"=>433790301059833691}
```
The `dict` generator retries if a key is duplicated. If it fails to generate a unique key after too many tries, it gives up by raising an error:
```ruby > Rantly { dict { ["a",integer] }} Rantly::TooManyTries: Exceed gen limit 60: 60 failed guards) ```
# Property Testing
Rantly extends Test::Unit and MiniTest::Test (5.0)/MiniTest::Unit::TestCase (< 5.0) for property testing. The extensions are in their own modules. So you need to require them explicitly:
```ruby require ‘rantly/testunit_extensions’ # for ‘test/unit’ require ‘rantly/minitest_extensions’ # for ‘minitest’ require ‘rantly/rspec_extensions’ # for RSpec ```
They define:
```ruby Test::Unit::Assertions#property_of(&block)
The block is used to generate random data with a generator. The method returns a Rantly::Property instance, that has the method 'check'.
```
Property assertions within Test::Unit could be done like this,
```ruby # checks that integer only generates fixnum. property_of {
integer
}.check { |i|
assert(i.is_a?(Integer), "integer property did not return Integer type")
} ```
Property assertions within Minitest could be done like this,
```ruby # checks that integer only generates fixnum. property_of {
integer
}.check { |i|
assert_kind_of Integer, i, "integer property did not return Integer type"
} ```
Property assertions within RSpec could be done like this,
```ruby # checks that integer only generates fixnum. it "integer property only returns Integer type" do
property_of { integer }.check { |i| expect(i).to be_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 Rantly#array generates the right sized array, I could say,
```ruby property_of {
len = integer [len,array(len){integer}]
}.check { |(len,arr)|
assert_equal len, arr.length
} ```
To control the number of property tests to generate, you have three options. In order of precedence:
```ruby property_of {
integer
}.check(9000) { |i|
assert_kind_of Integer, i
} ```
```ruby RANTLY_COUNT=9000 ruby my_property_test.rb ```
If you wish to have quiet output from Rantly, set environmental variable: ```ruby RANTLY_VERBOSE=0 # silent RANTLY_VERBOSE=1 # verbose and default if env is not set ``` This will silence the puts, print, and pretty_print statements in property.rb.
# Shrinking
Shrinking reduces the value of common types to some terminal lower bound. These functions are added to the Ruby types `Integer`, `String`, `Array`, and `Hash`.
For example a `String` is shrinkable until it is empty (e.g. `""`),
```ruby "foo".shrinkable? # => true "foo".shrink # => "fo" "fo".shrink # => "f" "f".shrink # => "" "".shrinkable? # => false ```
Shrinking allows `Property#check` to find a reduced value that still fails the condition. The value is not truely minimal because:
but is usually reduced enough to start debugging.
Enable shrinking with
```ruby require ‘rantly/shrinks’ ```
Use `Tuple` class if you want an array whose elements are individually shrinked, but are not removed. Example:
```ruby property_of {
len = range(0, 10) Tuple.new( array(len) { integer } )
}.check {
# .. property check here ..
} ```
Use `Deflating` class if you want an array whose elements are individully shrinked whenever possible, and removed otherwise. Example:
```ruby property_of {
len = range(0, 10) Deflating.new( array(len) { integer } )
}.check {
# .. property check here ..
} ```
Normal arrays or hashes are not shrinked.
# Contributors
Thanks to [all contributors](github.com/rantly-rb/rantly/graphs/contributors). :cupid: New contributors are welcome! :wink:
# License
Code published under MIT License, Copyright (c) 2009 Howard Yeh. See [LICENSE](github.com/abargnesi/rantly/LICENSE).