output_failure.txt

$ ruby test_pty.rb ./ex19
[child] You enter the The great hall.
[child] 
[child] > 
--(interaction)--
[child] You can go:
[child] NORTH
[child] 
[child] > 
--(interaction)--
[child] The throne room.
[child] 
[child] > 
 (RuntimeError)n `assert': Expected "The throne room.

> " to match (?-mix:^You go north, into:)
	from test_pty.rb:13:in `assert_match'
	from test_pty.rb:42:in `block (2 levels) in <main>'
	from test_pty.rb:37:in `each'
	from test_pty.rb:37:in `block in <main>'
	from test_pty.rb:35:in `spawn'
	from test_pty.rb:35:in `<main>'

output_success.txt

$ ruby test_pty.rb ./ex19
[child] You enter the The great hall.
[child] 
[child] > 
--(interaction)--
[child] You can go:
[child] NORTH
[child] 
[child] > 
--(interaction)--
[child] You go north, into:
[child] The throne room.
[child] 
[child] > 

test_pty.rb

# Buggy: misses output sometimes

require 'pty'

MAX_OUTPUT_SIZE = 4096

def assert(exp)
  raise yield unless exp
  true
end

def assert_match(actual, regex)
  assert(actual =~ regex) { "Expected \"#{actual}\" to match #{regex}" }
end

def read_output(io)
  buffer = ''
  until buffer =~ /\n> /
    io.readpartial MAX_OUTPUT_SIZE, buffer
  end
  buffer
end

def echo_output(str)
  str.split("\n").each do |line|
    puts "[child] #{line}"
  end
end

commands = [
            ['l', /^NORTH/],
            ['n', /^You go north, into:/]
]

PTY.spawn(ARGV.join(' ')) do |read_io, write_io, pid|
  echo_output read_output(read_io)
  commands.each do |input, expectation|
    puts "--(interaction)--"
    write_io.puts input
    actual_output = read_output read_io
    echo_output actual_output
    assert_match actual_output, expectation
  end
end