Behaviour not getting picked up

[ashton314]

Consider this code from chorex_test.exs at 6c47aeb:

defmodule TestChor1Unsplatting do
  defchor [Buyer1us, Seller1us] do
    def run() do
      Buyer1us.get_book_title() ~> Seller1us.(b)
      Seller1us.get_price("book:" <> b) ~> Buyer1us.(p)
      Seller1us.order_book(b)
      Buyer1us.(p + 2)
    end
  end
end

defmodule MyBuyer1Unsplatting do
  use TestChor1Unsplatting.Chorex, :buyer1us

  def get_book_title(), do: "Das Glasperlenspiel"
end

defmodule MySeller1Unsplatting do
  use TestChor1Unsplatting.Chorex, :seller1us

  def get_price("book:Das Glasperlenspiel"), do: 40
  def get_price("Das Glasperlenspiel"), do: 39
  def get_price(_), do: 0
end

test "choreography unsplat runs" do
  Chorex.start(TestChor1Unsplatting.Chorex,
               %{Buyer1us => MyBuyer1Unsplatting,
               Seller1us => MySeller1Unsplatting},
               [])
  assert_receive {:chorex_return, Buyer1us, 42}
  assert_receive {:chorex_return, Seller1us, 19}
end

I should be getting a compile time error that order_book is not implemented as a callback, but instead I'm getting a runtime explosion.

Maybe it's because it's an .exs file?