t.rb

require 'rspec'
require 'rspec/autorun'

def pack_size(desc)
  if (desc.match(/([\d]+)[\s]pack/i))
    $1.to_i
  else
    1
  end
end

describe 'pack_size' do
  it "lowercase 'pack'" do
    expect(pack_size("10 pack")).to eq 10
  end
  it "leading characters" do
    expect(pack_size("oh hai there 3 pack")).to eq 3
  end

  it "trailing characters" do
    expect(pack_size("10 Pack late to the show")).to eq 10
  end

  it "defaults to 1" do
    expect(pack_size("Nothing to see here")).to eq 1
  end
end