Game of Life Kata TDD Workshop

This repo contains an exercise for the tenth workshop - our first Code Retreat. This workshop is about developer skills. For this session we have based our activities on the Game of Life Code Retreat.

We've restructured the repository to provide a quick-start to TDD with RSpec and to mimic the setup we have been using in the workshops. The code to be created is found in the lib/ directory, and we have supplied unit tests in the spec/ directory.

There is a Sparse Matrix approach in the 'rhn' branch. This was created in the Code Retreat at Ruby Hack Night on September 30, 2015. Thanks to Mark Campbell of The Score for valuable input and guidance.

###Setup

Here are the steps to get you started with the repo. We assume, naturally, that you have a working development machine with Ruby 1.9 or better on it. At Ryatta Group we use rbenv, and so we've included some optional elements - just skip them if you're using rvm or are not versioning your Ruby.

% git clone git@github.com:k00ka/game-of-life.git
% cd game-of-life
% gem install bundler
Fetching: bundler-1.7.4.gem (100%)
Successfully installed bundler-1.7.4
1 gem installed
% bundle
Fetching gem metadata from https://rubygems.org/.........
Resolving dependencies...
Installing rake 10.3.2
...
Using bundler 1.7.4
Your bundle is complete!
Use `bundle show [gemname]` to see where a bundled gem is installed.

######Note: if you use rbenv...

% rbenv rehash

You are (almost) there!

###TDD If you want to learn (more) about TDD, there are plenty of online resources. For a quick primer, you can review our blog post from the previous workshop: [http://www.ryatta.com/refactoring-in-context/]

Tonight (or below if you're doing this exercise on your own), I’m going to give you some directions for what your solution should do. In response to these requests, you are going to:

Write a test or tests that translate my request into code
Demonstrate to yourself that those test(s) fail
Implement modifications to make the tests pass
Share your implementation with the team

We'll iterate on this pattern about 11 times so you can practice the TDD workflow.

####Tips

Implement the simplest code you can imagine to make the tests pass.
Once the tests pass, refactor the code to simplify it.
Let earlier tests stand, they will catch regressions.
Discuss edge cases and obscure aspects with the customer or others on your team.

###How to test

There is an empty file (well, almost empty) in the lib/ directory. It is called game_of_life.rb. This is part 1 of your deliverable.

There is a unit test file in the spec/ directory called game_of_life_spec.rb. This is part 2 of your deliverable.

To play the Game of Life, you need to make both files work together. To run the tests we have written against the code we've developed, do the following:

% rspec
F

Failures:

  1) GameOfLife#something returns an empty board given an empty board
     Failure/Error: expect(GameOfLife.step(empty_board)).to eq(empty_board)
     NameError:
       undefined local variable or method `empty_board' for #<RSpec::ExampleGroups::GameOfLifeSomething:0x007faad89e3ec0>
     # ./spec/game_of_life_spec.rb:11:in `block (2 levels) in <top (required)>'

Finished in 0.00052 seconds (files took 0.08027 seconds to load)
1 example, 1 failure

Failed examples:

rspec ./spec/game_of_life_spec.rb:10 # GameOfLife#something returns an empty board given an empty board

The text 1 failure means you're currently failing! Now go fix some code and share what you've learned with the group.

###How to play The universe of the Game of Life is an infinite two-dimensional orthogonal grid of square cells, each of which is in one of two possible states, live or dead. Every cell interacts with its eight neighbors, which are the cells that are directly horizontally, vertically, or diagonally adjacent. At each step in time, the following transitions occur:

Any live cell with fewer than two live neighbours dies, as if caused by underpopulation.
Any live cell with more than three live neighbours dies, as if by overcrowding.
Any live cell with two or three live neighbours lives on to the next generation.
Any dead cell with exactly three live neighbours becomes a live cell.

The initial pattern constitutes the seed of the system. The first generation is created by applying the above rules simultaneously to every cell in the seed?births and deaths happen simultaneously, and the discrete moment at which this happens is sometimes called a tick (in other words, each generation is a pure function of the one before). The rules continue to be applied repeatedly to create further generations.