Solution to http://tutorials.jumpstartlab.com/projects/eventmanager.html#iteration:-clean-phone-numbers

format_phone_number_test.rb

require 'minitest/autorun'
require 'minitest/pride'

class FormatPhoneNumber
  class BadNumberError < StandardError
  end

  def initialize(raw_number)
    @raw_number = raw_number
  end

  def call
    if digits.size < 10
      raise BadNumberError
    elsif digits.size == 11 && digits[0] == '1'
      hyphenate digits[1..-1]
    elsif digits.size >= 11
      raise BadNumberError
    else
      hyphenate digits
    end
  end

  private

  def hyphenate(digits)
    area_code = digits[0..2]
    exchange  = digits[3..5]
    extension = digits[6..-1]
    "#{area_code}-#{exchange}-#{extension}"
  end

  def digits
    raw_number.gsub(/\D/, '')
  end

  def raw_number
    @raw_number
  end
end

class SomeTest < Minitest::Test
  BadNumberError = FormatPhoneNumber::BadNumberError

  def format(number)
    FormatPhoneNumber.new(number).call
  end

  def test_removes_non_digits_and_hyphenates
    assert_equal "111-222-3333", format("   sjdklfsdj 1 lk1 kj1 ---22.2-/.,,nm33 3k3")
  end

  def test_raises_bad_number_error_when_less_than_10_digits
    assert_raises BadNumberError do
      format("1" * 9)
    end

    format("1" * 10)
  end

  def test_ignores_leading_1_on_11_digit_numbers
    assert_equal "234-567-8901", format("12345678901")
  end

  def test_raises_bad_number_error_when_11_digits_and_first_number_isnt_1
    assert_raises BadNumberError do
      format("23456789012")
    end
  end

  def test_raises_bad_number_error_when_greater_than_11_digits
    assert_raises BadNumberError do
      format("123456789012")
    end
  end
end