elixir argument error...

better_way_to_do_this.exs

    test "single digits" do
      %{zero: 0, one: 1, two: 2, three: 3, four: 4, five: 5, six: 6, seven: 7, eight: 8, nine: 9}
      |>
      Enum.each(fn {word, num} ->
        IO.puts "asserting #{word} == #{num}"
        assert to_string(word) == NumbersToWords.parse(num)
      end)
    end
    
    # I keep getting an argument error as it ends up trying to do :erlang.integer_to_binary("8")
    # instead of :erlang.integer_to_binary(8)... Probably due to how the "assert" macro works... How to fix?