by Nedomas

Nedomas / zapata

An Automatic Automated Test Writer

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Who has time to write tests? This is a revolutionary tool to make them write themselves.

Gem Version Build Status Dependency Status Coverage Status

Emiliano Zapata

What is your problem?

There comes a day where you have this bullshit class

. We need tests. :shipit:
class RobotToTest
  def initialize(human_name, cv)
    @name = robot_name(human_name)

def robot_name(human_name) "#{self.class.prefix}_#{human_name}" end

def cv { planets: planets } end

def nested_fun_objects(fun_objects) 'It was fun' end

def self.prefix 'Robot' end


def planets ['Mars', Human.home] end

def fun_objects [%i(array in array), { hash: nested_hash }] end

def nested_hash { in_hash: { in: array } } end

def array %w(array) end end

just another class to analyze

class Human def initialize human_name = 'Emiliano' end

def self.home 'Earth' end end

Solving it

You run

zapata generate app/models/robot_to_test.rb
and pop the champagne. Zapata generated
for you.
describe RobotToTest do
  let(:robot_to_test) do'Emiliano', { planets: ['Mars', Human.home] })

it '#robot_name' do expect(robot_to_test.robot_name('Emiliano')).to eq('Robot_Emiliano') end

it '#cv' do expect( eq({ planets: ['Mars', 'Earth'] }) end

it '#nested_fun_objects' do expect(robot_to_test.nested_fun_objects([ [:array, :in, :array], { hash: { in_hash: { in: ['array'] } } } ])).to eq('It was fun') end

it '#prefix' do expect(RobotToTest.prefix).to eq('Robot') end end

What does it do?

It tries to write a passing RSpec spec off the bat. It does fancy analysis to predict the values it could feed to the API of a class.

To be more specific: - Analyzes all vars and methods definitions in

- Checks what arguments does a testable method in
need - Searches for such variable or method name in methods in analyzed - Selects the most probable value by how many times it was repeated in code - Runs the RSpec and fills in the expected values of the test with those returned by RSpec

For more things it can currently do check test files

Workflow with Zapata

Say you are writing some new feature on your existing project. Before writing that, you probably want to test out the current functionality. But who has time for that?

You let Zapata create that quick spec for you. Think of it as a current functionality lock. Write more code and when you're happy with the result - lock it up again.


  • Ruby 2.1+
  • Rails 3.0+



to your
. It currently only works if the library is added to the
gem 'zapata', groups: %w(development test)


To use run

zapata generate app/models/model_name.rb

To ignore other files and analyze a single model you want to generate a spec for:

zapata generate app/models/model_name.rb --single

Collaboration :heart:

It is encouraged by somehow managing to bring a cake to your house. I promise, I will really try.

This is a great project to understand language architecture in general. A project to let your free and expressionistic side shine through by leaving meta hacks and rainbows everywhere.

Thank you to everyone who do. I strongly believe that this can make the developer job less robotic and more creative.

  1. Fork it
  2. Create your feature branch (
    git checkout -b my-new-feature
  3. Commit your changes (
    git commit -am 'Add some feature'
  4. Push to the branch (
    git push origin my-new-feature
  5. Create a new Pull Request

To install, run:

cd zapata

For specs:



bundle exec rspec --pattern "spec/*_spec.rb"


I am well aware that this is featured in Ruby Weekly 223. On that note I'd like to thank everybody who helped it shine through.

Special thanks to my comrade @jpalumickas, with whom we share a vision of a better world. Also - thank you @edgibbs, for being the early contributor. @morron - for caring.

Huge thanks to @marcinruszkiewicz for reviving this gem to life in 2019/2020. Also additional thanks to @jpalumickas for all the extra fixes and modernizing the codebase. This would not be done without you all.


Copyright (c) 2014-2018 Justas, Andrew, Ed, Dmitry, Domas. See LICENSE for details.

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