gistfile1.rb

require 'minitest/spec'
require 'minitest/autorun'

describe "Capture" do
  it "should capture all output in the same process" do
    out, err = capture_io do
      puts "STDOUT"
      warn "STDERR"
    end

    assert_equal "STDOUT\n", out
    assert_equal "STDERR\n", err
  end

  # This test isn't capture output and get failure
  it "should capture all output in subprocess" do
    out, err = capture_io do
      system("echo 'STDOUT'")
      system("echo 'STDERR' 1>&2")
    end
  
    assert_equal "STDOUT\n", out
    assert_equal "STDERR\n", err
  end

  it "should capture all output in subprocess with new method" do
    out, err = new_capture_io do
      system("echo 'STDOUT'")
      system("echo 'STDERR' 1>&2")
    end

    assert_equal "STDOUT\n", out
    assert_equal "STDERR\n", err
  end

  # I think we can replace `capture_io`
  # or add another realization
  def new_capture_io
    require 'tempfile'

    stdout, stderr = Tempfile.new(""), Tempfile.new("")
    orig_stdout, orig_stderr = STDOUT.dup, STDERR.dup
    STDOUT.reopen(stdout)
    STDERR.reopen(stderr)

    yield

    STDOUT.rewind
    STDERR.rewind
    return STDOUT.read, STDERR.read
  ensure
    stdout.unlink
    stderr.unlink

    STDOUT.reopen(orig_stdout)
    STDERR.reopen(orig_stderr)
  end
end

@route you can use StringIO instead of Tempfile to avoid disk IO.

@sobrinho let's move to minitest/minitest#161