diff --git a/lib/ex_unit/lib/ex_unit/capture_io.ex b/lib/ex_unit/lib/ex_unit/capture_io.ex
new file mode 100644
index 00000000000..c6893928722
--- /dev/null
+++ b/lib/ex_unit/lib/ex_unit/capture_io.ex
@@ -0,0 +1,171 @@
+defmodule ExUnit.CaptureIO do
+  @moduledoc """
+  This module provides functionality to capture IO to test it.
+  The way to use this module is to import them into your module.
+
+  ## Examples
+
+      defmodule AssertionTest do
+        use ExUnit.Case
+
+        import ExUnit.CaptureIO
+
+        test :example do
+          assert capture_io(fn ->
+            IO.puts "a"
+          end) == "a\n"
+        end
+      end
+
+  """
+
+  @doc """
+  Captures IO. Returns nil in case of no output.
+  Otherwise returns the binary which is captured outputs.
+  The input is mocked to return :eof.
+
+  ## Examples
+
+      iex> capture_io(fn -> IO.write "josé" end) == "josé"
+      true
+      iex> capture_io(fn -> :ok end) == nil
+      true
+
+  """
+  def capture_io(fun) do
+    original_gl = :erlang.group_leader
+    capture_gl = new_group_leader(self)
+
+    :erlang.group_leader(capture_gl, self)
+    fun.()
+    :erlang.group_leader(original_gl, self)
+
+    group_leader_sync(capture_gl)
+  end
+
+  defp new_group_leader(runner) do
+    spawn_link(fn -> group_leader_process(runner) end)
+  end
+
+  defp group_leader_process(runner) do
+    group_leader_loop(runner, :infinity, [])
+  end
+
+  defp group_leader_loop(runner, wait, buf) do
+    receive do
+      { :io_request, from, reply_as, req } ->
+        p = :erlang.process_flag(:priority, :normal)
+        buf = io_request(from, reply_as, req, buf)
+        :erlang.process_flag(:priority, p)
+        group_leader_loop(runner, wait, buf)
+      :stop ->
+        receive after: (2 -> :ok)
+        :erlang.process_flag(:priority, :low)
+        group_leader_loop(runner, 0, buf)
+      _ ->
+        group_leader_loop(runner, 0, buf)
+    after wait ->
+      :erlang.process_flag(:priority, :normal)
+      runner <- { self, buffer_to_result(buf) }
+    end
+  end
+
+  defp group_leader_sync(gl) do
+    gl <- :stop
+
+    receive do
+      { ^gl, buf } -> buf
+    end
+  end
+
+  defp io_request(from, reply_as, req, buf) do
+    { reply, buf1 } = io_request(req, buf)
+    io_reply(from, reply_as, reply)
+    buf1
+  end
+
+  defp io_reply(from, reply_as, reply) do
+    from <- { :io_reply, reply_as, reply }
+  end
+
+  defp io_request({ :put_chars, chars }, buf) do
+    { :ok, [chars|buf] }
+  end
+
+  defp io_request({ :put_chars, m, f, as }, buf) do
+    chars = apply(m ,f, as)
+    { :ok, [chars|buf] }
+  end
+
+  defp io_request({ :put_chars, _enc, chars }, buf) do
+    io_request({ :put_chars, chars }, buf)
+  end
+
+  defp io_request({ :put_chars, _enc, mod, func, args }, buf) do
+    io_request({ :put_chars, mod, func, args }, buf)
+  end
+
+  defp io_request({ :get_chars, _enc, _propmpt, _n }, buf) do
+    { :eof, buf }
+  end
+
+  defp io_request({ :get_chars, _prompt, _n }, buf) do
+    { :eof, buf }
+  end
+
+  defp io_request({ :get_line, _prompt }, buf) do
+    { :eof, buf }
+  end
+
+  defp io_request({ :get_line, _enc, _prompt }, buf) do
+    { :eof, buf }
+  end
+
+  defp io_request({ :get_until, _prompt, _m, _f, _as }, buf) do
+    { :eof, buf }
+  end
+
+  defp io_request({ :setopts, _opts }, buf) do
+    { :ok, buf }
+  end
+
+  defp io_request(:getopts, buf) do
+    { { :error, :enotsup }, buf }
+  end
+
+  defp io_request({ :get_geometry, :columns }, buf) do
+    { { :error, :enotsup }, buf }
+  end
+
+  defp io_request({ :get_geometry, :rows }, buf) do
+    { { :error, :enotsup }, buf }
+  end
+
+  defp io_request({ :requests, reqs }, buf) do
+    io_requests(reqs, { :ok, buf })
+  end
+
+  defp io_request(_, buf) do
+    { { :error, :request }, buf }
+  end
+
+  defp io_requests([r|rs], { :ok, buf }) do
+    io_requests(rs, io_request(r, buf))
+  end
+
+  defp io_requests(_, result) do
+    result
+  end
+
+  defp buffer_to_result([]) do
+    nil
+  end
+
+  defp buffer_to_result([bin]) when is_binary(bin) do
+    bin
+  end
+
+  defp buffer_to_result(buf) do
+    buf |> :lists.reverse |> list_to_binary
+  end
+end
diff --git a/lib/ex_unit/test/ex_unit/capture_io_test.exs b/lib/ex_unit/test/ex_unit/capture_io_test.exs
new file mode 100644
index 00000000000..e799aad219f
--- /dev/null
+++ b/lib/ex_unit/test/ex_unit/capture_io_test.exs
@@ -0,0 +1,160 @@
+Code.require_file "../test_helper.exs", __DIR__
+
+defmodule ExUnit.CaptureIOTest.Value do
+  def binary, do: "a"
+end
+
+alias ExUnit.CaptureIOTest.Value
+
+defmodule ExUnit.CaptureIOTest do
+  use ExUnit.Case, async: true
+
+  doctest ExUnit.CaptureIO, import: true
+
+  import ExUnit.CaptureIO
+
+  test :capture_io_with_nothing do
+    assert capture_io(fn ->
+    end) == nil
+  end
+
+  test :capture_io_with_put_chars do
+    assert capture_io(fn ->
+      :io.put_chars("")
+    end) == ""
+
+    assert capture_io(fn ->
+      :io.put_chars("a")
+      :io.put_chars("b")
+    end) == "ab"
+
+    assert capture_io(fn ->
+      send_and_receive_io({ :put_chars, :unicode, Value, :binary, [] })
+    end) == "a"
+
+    assert capture_io(fn ->
+      :io.put_chars("josé")
+    end) == "josé"
+
+    assert capture_io(fn ->
+      assert :io.put_chars("a") == :ok
+    end)
+  end
+
+  test :capture_io_with_put_chars_to_stderr do
+    assert capture_io(fn ->
+      :io.put_chars(:standard_error, "a")
+    end) == nil
+  end
+
+  test :capture_io_with_get_chars do
+    assert capture_io(fn ->
+      :io.get_chars(">", 3)
+    end) == nil
+
+    capture_io(fn ->
+      assert :io.get_chars(">", 3) == :eof
+    end)
+  end
+
+  test :capture_io_with_get_line do
+    assert capture_io(fn ->
+      :io.get_line ">"
+    end) == nil
+
+    capture_io(fn ->
+      assert :io.get_line(">") == :eof
+    end)
+  end
+
+  test :capture_io_with_get_until do
+    assert capture_io(fn ->
+       send_and_receive_io({ :get_until, '>', :m, :f, :as })
+    end) == nil
+
+    capture_io(fn ->
+       assert send_and_receive_io({ :get_until, '>', :m, :f, :as }) == :eof
+    end)
+  end
+
+  test :capture_io_with_setopts do
+    assert capture_io(fn ->
+      :io.setopts({ :encoding, :latin1 })
+    end) == nil
+
+    capture_io(fn ->
+      assert :io.setopts({ :encoding, :latin1 }) == :ok
+    end)
+  end
+
+  test :capture_io_with_getopts do
+    assert capture_io(fn ->
+      :io.getopts
+    end) == nil
+
+    capture_io(fn ->
+      assert :io.getopts == { :error, :enotsup }
+    end)
+  end
+
+  test :capture_io_with_columns do
+    assert capture_io(fn ->
+      :io.columns
+    end) == nil
+
+    capture_io(fn ->
+      assert :io.columns == { :error, :enotsup }
+    end)
+  end
+
+  test :capture_io_with_rows do
+    assert capture_io(fn ->
+      :io.rows
+    end) == nil
+
+    capture_io(fn ->
+      assert :io.rows == { :error, :enotsup }
+    end)
+  end
+
+  test :capture_io_with_multiple_io_requests do
+    assert capture_io(fn ->
+      send_and_receive_io({ :requests, [{ :put_chars, :unicode, "a" },
+                                        { :put_chars, :unicode, "b" }]})
+    end) == "ab"
+
+    capture_io(fn ->
+      assert send_and_receive_io({ :requests, [{ :put_chars, :unicode, "a" },
+                                               { :put_chars, :unicode, "b" }]}) == :ok
+    end)
+  end
+
+  test :caputure_io_with_unknown_io_request do
+    assert capture_io(fn ->
+      send_and_receive_io(:unknown)
+    end) == nil
+
+    capture_io(fn ->
+      assert send_and_receive_io(:unknown) == { :error, :request }
+    end)
+  end
+
+  test :capture_io_with_inside_assert do
+    try do
+      capture_io(fn ->
+        assert false
+      end)
+    rescue
+      error in [ExUnit.AssertionError] ->
+        "Expected false to be true" = error.message
+    end
+  end
+
+  defp send_and_receive_io(req) do
+    :erlang.group_leader <- { :io_request, self, self, req }
+    s = self
+    receive do
+      { :io_reply, ^s, res} -> res
+    end
+  end
+end