Quickly hack an algorithm with a TDD template

Thursday 9 January 2014

TL;DR - I created ssaunier/lab to start hacking even faster!

A few days ago, I was on a phone interview, with my screen shared. I was asked to write an algorithm, and I had 20 minutes. I decided to go with Ruby, and TDD. But I spent 15 minutes to correctly setup the environment with guard rspec before actually working on the algorithm. With these instructions, I would have had 19 minutes.

$ mkdir lab && cd $_
$ echo "source 'https://rubygems.org'\ngem 'guard-rspec'" > Gemfile
$ bundle install
$ bundle exec guard init
$ echo "--color" > .rspec
$ mkdir -p lib spec/lib

The interview problem was:

Devise a function that takes an integer and returns a string that
is the decimal representation of that number grouped by commas
after every 3 digits. For instance:
1 -> "1"
1000 -> "1,000"
57154351 -> "57,154,351"

Let’s code this feature in an IntegerFormatter class, so let’s create our files:

$ echo "class IntegerFormatter\nend" > lib/integer_formatter.rb
$ echo "require './lib/integer_formatter'\n" >> spec/lib/integer_formatter_spec.rb
$ echo "describe IntegerFormatter do\nend" >> spec/lib/integer_formatter_spec.rb

I could also just have touched both files and add some code afterwards.

Open the lab folder in your favorite text editor, then run guard. It will automatically relaunch your specs on each file change. Very handy for the red / green cycle of TDD.

$ bundle exec guard

Now go hack your solution! FWIW, here’s mine :)

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