Roman Numerals kata implemented in elixir

roman_numerals.exs

defmodule RomanNumerals do

	@moduledoc """
	Task definition: Create a function taking a positive integer as its parameter and
	returning a string containing the Roman Numeral representation of that integer.
	"""
 
  	def convert(number) do
	    convert(number, [[10,'X'], [9,'IX'], [5,'V'], [4,'IV'], [1,'I']])
  	end  	

  	defp convert(0, _) do
	     ''
  	end

  	defp convert(number, [[arabic, roman]|_] = l) when number >= arabic do
	     roman ++ convert(number - arabic, l)
  	end

  	defp convert(number, [_|t]) do
	     convert(number, t)
  	end
end
 
ExUnit.start
 
defmodule RomanNumeralsTest do
  use ExUnit.Case
  
  test "converts arabic numbers to roman" do
  	Enum.each [ [1,'I'],
  		    [2,'II'],
		    [3,'III'],
  		    [4,'IV'],
  		    [5,'V'],
  		    [6,'VI'],
  		    [7,'VII'],
  		    [8,'VIII'],
  		    [9,'IX'],
  		    [10,'X'],
  		    [11,'XI'],
  		    [14,'XIV'],
  		    [19,'XIX'],
  		    [20,'XX'],
  		    [25,'XXV'],
  		    [27,'XXVII'] ], fn [arabic, roman] ->
  		assert roman == RomanNumerals.convert(arabic)
  	end
  end
end

Sorry for the delay. I had expect notification on a reply from github.

It's my understanding that in elixir single quoted strings (char lists) often perform worse than double quoted strings (binaries). Not that it really matters in this small of a problem.

I copied your tests and worked from them. I'm sorry I didn't do intermediate check ins. I feel I need to defend my TDD skills to you. I gave a talk at JavaOne 2002 entitled "Unit Testing Made Easy: Design Principles to Facilitate Testing". I'm having trouble finding much information online about it, but here's 2 links, the first is my comment on the refactoring mailing list about it, and the 2nd is someone's notes of talks they attended:
http://osdir.com/ml/programming.refactoring/2002-07/msg00052.html
http://ziggr.com/javaone2002/#z51

I could have incrementally done red/green/refactor for this exercise. However, given the limited complexity of it, and the fact that I've done the roman numeral kata in several languages, I wouldn't learn anything but new elixir syntax. So, I just focused on that. I built off your "when number >= arabic" idea, then learned elixir syntax for div, rem, and String.duplicate