Curious mix test error

I have the following comment in my code:

  @doc """
  Divides a deck into a 'hand' and the remainder of the deck.
  The `hand_size` argument indicates how many cards to 'deal' from the deck.

  ## Examples

      iex> deck = Cards.create_deck(true)
      iex> {hand, deck} =, 1)
      ["Two of Spades"]


When I compile or recompile the file - all is well.
If I manually run the above listed iex> lines, one at a time, all is well.

If I run mix test I get this error report:

Compiling 1 file (.ex)
warning: variable "hand" does not exist and is being expanded to "hand()", please use parentheses to remove the ambiguity or change the variable name
  (for doctest at) lib/cards.ex:55

warning: variable "deck" is unused
  (for doctest at) lib/cards.ex:56

warning: variable "hand" is unused
  (for doctest at) lib/cards.ex:56

== Compilation error in file test/cards_test.exs ==
** (CompileError) (for doctest at) lib/cards.ex:55: undefined function hand/0
    (stdlib) lists.erl:1338: :lists.foreach/2
    (stdlib) erl_eval.erl:677: :erl_eval.do_apply/6
    (elixir) lib/code.ex:767: Code.require_file/2
    (elixir) lib/kernel/parallel_compiler.ex:209: anonymous fn/4 in Kernel.ParallelCompiler.spawn_workers/6

The reported lines 55 and 56 are the iex> lines in my comment.
I’m using Elixir v1.7.1
The cards_test.exs file is unchanged from what mix generated for my project.

What have I done wrong?

You have missed iex> preamble before hand in the 3rd line.

Also if you want to rebind 2nd element in the tuple in line 2, use _, otherwise pin {hand, ^deck}.


Yep - I just realized that after I wrote the question. Thanks!