capture std in/out/err

spec_helper.rb

def capture(*streams)
  require 'stringio'

  streams.map! { |stream| stream.to_s }
  begin
    result = StringIO.new
    streams.each { |stream| eval "$#{stream} = result" }
    yield
  ensure
    streams.each { |stream| eval("$#{stream} = #{stream.upcase}") }
  end
  result.string
end

capture(:stdout) {
    # do your thing
}