Test driving Conway's Game of Life in Ruby : Part I

Well I had Ruby on my to-learn list for some time now. The pickaxe (don't leave your ruby-home without it) was getting rusty in a corner. I also had another book, Data Structures and Program Design in C, something I had picked up for the interview of my first job. So I decided why not translate the examples in the latter in Ruby – two birds with one stone ??

One that I liked up front (Chapter 1) is Conway’s Game of Life. The rules are explained here along with some cool information. This is basically a “cellular automaton”.. sounds ultra nerdy doesn’t it? Don’t worry sounds as greek to me as it does to you. In simple terms, it is a simulation of a colony of cells evolving. There are some rules governing the birth and mortality of cells. See the wikipedia page for details

Anyways, the writeup is also present in the uploaded zip -
http://tech.groups.yahoo.com/group/testdrivendevelopment/files/
"TDD_Conways_GameOfLife_Ruby.zip"


Let’s begin.
First I need to figure out how to write a test in Ruby. Pick up the pickaxe… What the…. now it can’t be that easy… can it?
Let’s create a file called GameOfLife.rb. Important items in bold below

require "test/unit"
class Test_GameOfLife < Test::Unit::TestCase

 def test_GetOne
   assert_equal(1, GameOfLife.new.getOne);
 end
end


class GameOfLife
end


L:\Gishu\Ruby\GameOfLife>ruby GameOfLife.rb
Loaded suite GameOfLife
Started
E
Finished in 0.016 seconds.

 1) Error:
test_GetOne(Test_GameOfLife):
NoMethodError: undefined method `getOne' for #<GameOfLife:0x2ba14d8>
   GameOfLife.rb:5:in `test_GetOne'

1 tests, 0 assertions, 0 failures, 1 errors

Ok we have a code red !! Let’s get it green… quick to the test mobile..

require "test/unit"
class Test_GameOfLife < Test::Unit::TestCase

 def test_GetOne
   assert_equal(1, GameOfLife.new.getOne);
 end
end


class GameOfLife
end


L:\Gishu\Ruby\GameOfLife>ruby GameOfLife.rb
Loaded suite GameOfLife
Started
E
Finished in 0.016 seconds.

 1) Error:
test_GetOne(Test_GameOfLife):
NoMethodError: undefined method `getOne' for #<GameOfLife:0x2ba14d8>
   GameOfLife.rb:5:in `test_GetOne'

1 tests, 0 assertions, 0 failures, 1 errors

require "test/unit"
class Test_GameOfLife < Test::Unit::TestCase

def test_GetOne
   assert_equal(1, GameOfLife.new.getOne);
 end
end

class GameOfLife
 def getOne
   return 1
 end
end


L:\Gishu\Ruby\GameOfLife>ruby GameOfLife.rb
Loaded suite GameOfLife
Started
.
Finished in 0.0 seconds.

1 tests, 1 assertions, 0 failures, 0 errors

Woo hoo !!! I have my first green light in Ruby. I feel the confidence running through my veins now… I had heard about Ruby’s principle of least surprise.. I’m fascinated. Beam me up, Scotty !!

The advent of colonization
Let’s make the input to the program a file. This file would contain the current snapshot of a “colony” of cells. The first line in the file shall tell us the max rows and columns in the colony

Colony1.txt
3, 4

So we need a colony class that can tell us the bounds of a colony in an input file.
Colony.ReadFromFile - ReadBounds
Naming conventions : Test case classes are saved in files prefixed with tc_

tc_Colony.rb

require 'test/unit'
require 'Colony'

class Test_Colony < Test::Unit::TestCase

 def test_ReadFromFile
   c = Colony.readFromFile("Colony1.txt");
   assert_equal(3, c.maxRows);
   assert_equal(4, c.maxCols);
 end
end

Colony.rb
class Colony
 def Colony.readFromFile( sColonyFile )
 end
end

Green
Initialize is a method that would be called whenever a Colony.new is issued. We take in 2 parameters for maxRows and maxCols to know the bounds.

Colony.readFromFile: We also have our first taste of File I/O. We read the first line and use regular expressions to break the line into 2 parts. We convert them to integers via to_i() and use them to create a Colony instance.

class Colony
 attr_reader :maxRows, :maxCols

 def initialize( iRows, iCols )
   @maxRows=iRows
   @maxCols=iCols
 end

 def Colony.readFromFile( sColonyFile )
     sColonyRows = sColonyCols = ""
     File.open(sColonyFile) { |obFile|
       sDimensions = obFile.gets
       sColonyRows, sColonyCols = sDimensions.scan(/\d+/)
     }
     return Colony.new(sColonyRows.to_i, sColonyCols.to_i)
 end
end

Refactor
Inline the variable sDimensions.

def Colony.readFromFile( sColonyFile )
     sColonyRows = sColonyCols = ""
     File.open(sColonyFile) { |obFile|
       sColonyRows, sColonyCols = obFile.gets.scan(/\d+/)
     }
     return Colony.new(sColonyRows.to_i, sColonyCols.to_i)
end

Colony.IsCellAlive
Since I am new to this.. I wrote the “read from file” test in 2 parts. Part 2 – now we read the actual colony. Update the Colony1.txt file as follows

Colony1.txt
3, 4
0 0 0 0
1 1 0 0
0 0 0 1

Red

tc_Colony.rb
def test_IsCellAlive
   c = Colony.readFromFile("Colony1.txt");
   expected = [
     false, false, false, false,
     true, true, false, false,
     false, false, false, true ]
    
   iExpectedLooper = 0;
   (0...c.maxRows).each{ |iRow|
     (0...c.maxCols).each{ |iCol|
       assert_equal( expected[iExpectedLooper], c.isCellAlive( iRow, iCol ) )
       iExpectedLooper = iExpectedLooper.succ
     }
   }
end

Colony.rb
def isCellAlive( iRow, iCol )
   return false;
end

Now to show that I’m not making all this up…

L:\Gishu\Ruby\GameOfLife>ruby tc_Colony.rb
Loaded suite tc_Colony
Started
F.
Finished in 0.094 seconds.

 1) Failure:
test_IsCellAlive(Test_Colony)
   [tc_Colony.rb:23:in `test_IsCellAlive'
    tc_Colony.rb:21:in `each'
    tc_Colony.rb:21:in `test_IsCellAlive'
    tc_Colony.rb:20:in `each'
    tc_Colony.rb:20:in `test_IsCellAlive']:
<true> expected but was
<false>.

2 tests, 7 assertions, 1 failures, 0 errors

Green
String.scan can parse a line and return an array. So this should work for us…
sRow.scan(/\d/) - > [“0”, “0”, “0”, 0”]
So I build up a 2D Array like this and stash it away in the Colony object.
[ [“0”, “0”, “0”, 0”], [“1”, “1”, “0”, “0”], [“0”, “0”, ”0”, “1” ] ]

class Colony
 attr_reader :maxRows, :maxCols

 def initialize( iRows, iCols, obColony2DArray )
   @maxRows=iRows
   @maxCols=iCols
   @colonyGrid=obColony2DArray
 end

 def Colony.readFromFile( sColonyFile )
     sColonyRows = sColonyCols = ""
     ob2DArray ||= []
    
     File.open(sColonyFile) { |obFile|
       sColonyRows, sColonyCols = obFile.gets.scan(/\d+/)
      
       while(sRow = obFile.gets)
         ob2DArray.insert(-1, sRow.scan(/\d/) )
       end
     }
     return Colony.new(sColonyRows.to_i, sColonyCols.to_i, ob2DArray)
 end

 def isCellAlive( iRow, iCol )
   return  ( @colonyGrid[iRow][iCol] == "1" ? true : false )
 end
end

Refactor
For the ones who came in late, I can factor out common code into a setup method, which is guaranteed to be executed before every test. So off with duplication !!

Add a member variable @obColony and initialize it inside setup()

tc_Colony.rb

def setup
   @obColony = Colony.readFromFile("Colony1.txt");
end

to_s() – ToString() for the .Net ters
Red

def test_ToString
   assert_equal( ". . . . \n@ @ . . \n. . . @ \n",
     @obColony.to_s )
end

 1) Failure:
test_ToString(Test_Colony) [tc_Colony.rb:34]:
<". . . . \n@ @ . . \n. . . @ \n"> expected
but was
<"#<Colony:0x2b9c9a8>">.

Green

def to_s
   sGridListing = ""
   (0…maxRows).each{ |iRow|
     (0...maxCols).each{ |iCol|
       sGridListing += ( isCellAlive( iRow, iCol) ? "@ " : ". " )
      }
      sGridListing += "\n"
   }
   return sGridListing
end

On to Part 2