capturing output with UnitTest

test_helper.rb

require './test/additional_assertions'


additional_assertions.rb

module AdditionalAssertions
  module CaptureOutput
    # NOTE: MiniTest has capture_io and capture_subprocess_io
    # so when upgraded to MiniTest this should be replaced
    # with MiniTest methods
    # Use as:
    # out = capture_output { method_to_call(param1, param2) }
    # output = out[0], error = out[1] or
    # output = out.first, error = out.last
    def capture_output
      require 'stringio'

      captured_stdout, captured_stderr = StringIO.new, StringIO.new
      orig_stdout, orig_stderr = $stdout, $stderr
      $stdout, $stderr         =  captured_stdout, captured_stderr

      begin
        yield
      ensure
        $stdout = orig_stdout
        $stderr = orig_stderr
      end
      return captured_stdout.string, captured_stderr.string
    end

    def capture_subprocess_output
      require 'tempfile'

      captured_stdout, captured_stderr = Tempfile.new("out"), Tempfile.new("err")
      orig_stdout, orig_stderr = $stdout.dup, $stderr.dup
      $stdout.reopen captured_stdout
      $stderr.reopen captured_stderr

      begin
        yield

        $stdout.rewind
        $stderr.rewind

        [captured_stdout.read, captured_stderr.read]
      ensure
        captured_stdout.unlink
        captured_stderr.unlink
        $stdout.reopen orig_stdout
        $stdout.reopen orig_stderr
      end
    end
  end

  include CaptureOutput
end