Basic CoffeeScript + AngularJS Pig-latin filter + unit tests. Only moves first letter at the moment. AngularJS filters are my favorite TDD.

pig-latin-filter.coffee

'use strict';

angular.module('pig-latin', [])
  .filter 'pig-latin', () ->
    # input is handed into the filter
    (input) ->
      # equals itself or ''
      input ||= ''

      if input.length > 0
        # splits string based on char
        firstChar = input.slice(0, 1)
        theRest = input.slice(1)
        input = theRest + firstChar + "a"

      # returns input
      input

pig-latin-filter.spec.coffee

'use strict'

describe 'Pig Latin Filter', () ->
  # initialize a new instance of the filter before each test
  filter = {}

  # load the filter's module
  beforeEach module('pig-latin')

  # give our local object the magical injection
  beforeEach inject ($filter) ->
    filter = $filter 'pig-latin'

  # pretty existential, huh?
  it 'should have a filter', () ->
    expect(filter).not.toBe(null)

  # base case, handles no input
  it 'should return an empty string when given null', () ->
    output = filter()
    expect(output).toBe('')

  # simple test
  it 'should set "bozo" to "ozoba"', ->
    output = filter("bozo")
    expect(output).toBe("ozoba")