Generative

Generative testing for RSpec

Installation

Add Generative to your Gemfile (or gemspec):

group :test do
  gem 'generative'
  gem 'rspec'
end

...and then run bundle.

Require Generative in your .rspec file:

--color
--format progress
--require generative

Modify your Rakefile to create separate spec and generative tasks:

require 'bundler/gem_tasks'
require 'rspec/core/rake_task'

task default: [:spec, :generative]

RSpec::Core::RakeTask.new(:spec) do |t|
  t.rspec_opts = '--format documentation --tag ~generative --order random'
end

RSpec::Core::RakeTask.new(:generative) do |t|
  ENV['GENERATIVE_COUNT'] = '10_000'
  t.rspec_opts = '--format Generative --tag generative'
end

Remove any random/other ordering

If using RSpec 2, you'll need to make sure you remove config.order = 'random', or any other ordering strategies, from your spec helper.

In RSpec 3, this is not nessecary, because each example group (the generative block) can override ordering for that group.

Usage

Specs

In your tests, add a generative block. This is a essentially the same as a context or describe block. Inside the block, define some data as you would a let. Then, write your it/specify blocks as usual (while keeping in mind that the input could be anything).

describe String do
  let(:string) { "abc" }

  describe "#reverse" do
    it "reverses" do
      expect(string.reverse).to eq("cba")
    end

    generative do
      data(:string) { rand(12345).to_s }

      it "maintains length" do
        expect(string.reverse.length).to eq(string.length)
      end

      it "is not destructive" do
        expect(string.reverse.reverse).to eq(string)
      end
    end
  end
end

Now, run your tests with rake or rspec.

Number of Tests

Generative uses the GENERATIVE_COUNT environment variable to control how many tests to run for each example. It defaults to 100, and in the example Rakefile above, we set it to 10,000.

Formatters

Given the examples above, running rspec will use the default "progress" formatter. Requiring generative will modify this formatter to output blue dots instead of green for generative tests. Generative also includes it's own formatter, which will only display generative test names once, also in blue.