Testing IO from STDIN in Elixir

I’m quite stuck at something I thought would be quite straight forward, but it seems maybe this topic hasn’t come up much in my career in Elixir.

I am trying to run a test to check STOUT and test STDIN for a function:

test "can read and output" do
    input =
    """
    3
    Hello
    Hello World
    Hello A B World
    """
    assert ExUnit.CaptureIO.capture_io(fn ->
             IO.write(input)
            task = Task.async(Example, :start, [])
            Task.await(task)
           end) == """
    3
    Hello
    Hello World
    Hello B A World
    """
  end

Within my code I’ve been trying to read from stdin, but I keep getting :eof when I used IO.read(:line) or ""if I tryIO.read(:all)`.

I’m pretty sure I must be close, but I am missing something somewhere. The reason I’m launching a task is because I’m pretty sure the code will block so I’m unable to write to :stdio.

here’s my code for the function:

def start(pid \\ :stdio) do
    number_of_lines =
      IO.read(pid, :read)
      |> String.trim()
      |> String.to_integer()
    Enum.each(0..number_of_lines, fn _i ->
      sentence =
        IO.read(pid, :line)
        |> IO.inspect()
        |> String.trim()
        |> String.split()
      sentence_to_write =
        if length(sentence) > 2 do
          [hd | tail] = sentence
          {last, rest} = List.pop_at(tail, length(tail))
          new_tail = Enum.reverse(rest) ++ [last]
          [hd | new_tail]
        else
          sentence
        end
      sentence_to_write
      |> Enum.reduce(fn word, acc ->
        acc <> " " <> word
      end)
      |> IO.write(pid)
    end)
  end

The there’s a pid there is I was also thinking I can create a pid that responds to the message protocol for writing to a device, but I kind of gave up around there, thinking there must be a way to do this without creating another process.

Does anyone have any idea about how I can achieve this?