ExUnit v1.0.5 ExUnit.CaptureIO

Functionality to capture IO for testing.

Examples

defmodule AssertionTest do
  use ExUnit.Case

  import ExUnit.CaptureIO

  test "checking the return value and the IO output" do
    fun = fn ->
      assert Enum.each(["some", "example"], &(IO.puts &1)) == :ok
    end

    assert capture_io(fun) == "some\nexample\n"

    # Or use only: `capture_io(fun)` to silence the
    # IO output (so only assert the return value)
  end
end

Summary

Functions

capture_io(fun)

Captures IO generated when evaluating fun

capture_io(device, fun)

capture_io(device, input, fun)

Functions

capture_io(fun)

Captures IO generated when evaluating fun.

Returns the binary which is the captured output.

By default, capture_io replaces the group_leader (:stdio) for the current process. However, the capturing of any other named device, such as :stderr, is also possible globally by giving the registered device name explicitly as an argument.

Note that when capturing something other than :stdio, the test should run with async false.

When capturing :stdio, if the :capture_prompt option is false, prompts (specified as arguments to IO.get* functions) are not captured.

A developer can set a string as an input. The default input is :eof.

Examples

iex> capture_io(fn -> IO.write "john" end) == "john"
true

iex> capture_io(:stderr, fn -> IO.write(:stderr, "john") end) == "john"
true

iex> capture_io("this is input", fn ->
...>   input = IO.gets ">"
...>   IO.write input
...> end) == ">this is input"
true

iex> capture_io([input: "this is input", capture_prompt: false], fn ->
...>   input = IO.gets ">"
...>   IO.write input
...> end) == "this is input"
true

capture_io(device, fun)

capture_io(device, input, fun)