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EdgeCase Ruby Koans

The Ruby Koans walk you along the path to enlightenment in order to learn Ruby. The goal is to learn the Ruby language, syntax, structure, and some common functions and libraries. We also teach you culture. Testing is not just something we pay lip service to, but something we live. It is essential in your quest to learn and do great things in the language.

The Structure

The koans are broken out into areas by file, hashes are covered in about_hashes.rb, modules are introduced in about_modules.rb, etc. They are presented in order in the path_to_enlightenment.rb file.

Each koan builds up your knowledge of Ruby and builds upon itself. It will stop at the first place you need to correct.

Some koans simply need to have the correct answer substituted for an incorrect one. Some, however, require you to supply your own answer. If you see the method __ (a double underscore) listed, it is a hint to you to supply your own code in order to make it work correctly.

Installing Ruby

If you do not have Ruby setup, please visit for operating specific instructions. In order to run this you need ruby and rake installed. To check the installations simply type:

*nix platforms from any terminal window:

[~] $ ruby --version
[~] $ rake --version

Windows from the command prompt (cmd.exe)

c:\ruby --version
c:\rake --version

Any response for Ruby with a version number greater than 1.8 is fine (should be around 1.8.6 or more). Any version of rake will do.

The Path To Enlightenment

You can run the tests through rake or by calling the file itself (rake is the recommended way to run them as we might build more functionality into this task).

*nix platforms, from the koans directory

[ruby_koans] $ rake                           # runs the default target :walk_the_path
[ruby_koans] $ ruby path_to_enlightenment.rb  # simply call the file directly

Windows is the same thing

c:\ruby_koans\rake                             # runs the default target :walk_the_path
c:\ruby_koans\ruby path_to_enlightenment.rb    # simply call the file directly

Red, Green, Refactor

In test-driven development the mantra has always been, red, green, refactor. Write a failing test and run it (red), make the test pass (green), then refactor it (that is look at the code and see if you can make it any better. In this case you will need to run the koan and see it fail (red), make the test pass (green), then take a moment and reflect upon the test to see what it is teaching you and improve the code to better communicate its intent (refactor).

The very first time you run it you will see the following output:

[ ruby_koans ] $ rake
(in /Users/person/dev/ruby_koans)
cd koans

Thinking AboutAsserts
  test_assert_truth has damaged your karma.

You have not yet reached enlightenment ...
<false> is not true.

Please meditate on the following code:
./about_asserts.rb:10:in `test_assert_truth'

mountains are merely mountains

You have come to your first stage. If you notice it is telling you where to look for the first solution:

Please meditate on the following code:
./about_asserts.rb:10:in `test_assert_truth'

We then open up the about_asserts.rb file and look at the first test:

# We shall contemplate truth by testing reality, via asserts.
def test_assert_truth
  assert false                # This should be true

We then change the false to true and run the test again. After you are done, think about what you are learning. In this case, ignore everything except the method name (test_assert_truth) and the parts inside the method (everything before the end).

In this case the goal is for you to see that if you pass a value to the assert method, it will either ensure it is true and continue on, or fail if in fact the statement is false.


A special thanks to Mike Clark and Ara Howard for inspiring this project. Mike Clark wrote an excellent blog post about learning Ruby through unit testing. This sparked an idea that has taken a bit to solidify, that of bringing new rubyists into the community through testing. Ara Howard then gave us the idea for the Koans in his ruby quiz entry on Meta Koans (a must for any rubyist wanting to improve their skills). Also, “The Little Lisper” taught us all the value of the short questions/simple answers style of learning.

Mike Clark's post

Meta Koans

The Little Lisper

Other Resources

The Ruby Language

Try Ruby in your browser

Dave Thomas' introduction to Ruby Programming Ruby (the Pick Axe)

Brian Marick's fantastic guide for beginners Everyday Scripting with Ruby

Other stuff


Jim Weirich <>


Joe O'Brien <>

Issue Tracker


Ruby 1.8.x or later and Rake (any recent version)


A set of Koans to teach the Ruby language




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