request_test.rb

#!/usr/bin/env ruby

require 'rack'
require 'net/http'
require 'uri'

def request_test(request_timeout = 3)
  unused_port = -> do
    s = TCPServer.open(0)
    port = s.addr[1]
    s.close
    port
  end.()

  read, write = IO.pipe
  response    = ->(env) { [200, {'Content-Type' => 'text/plain'}, ['ok']] }

  instance = Class.new {
    define_method(:uri)      { URI.parse("http://localhost:#{unused_port}") }
    define_method(:request)  {|&block| @request = block }
    define_method(:request!) { @request.() }
    define_method(:response) {|&block| response = block }
  }.new

  Proc.new.(instance)

  pid = fork do
    Rack::Handler::WEBrick.run \
      ->(env) {
        Marshal.dump(env.select{|k, v| ('A'..'Z').include?(k[0]) }, write)
        write.close

        response.(env)
      },
      Port:      unused_port,
      Logger:    WEBrick::Log.new("/dev/null"),
      AccessLog: []
  end

  sleep 1

  instance.request!

  timeout(request_timeout) {
    Marshal.load(read)
  }
ensure
  write.close unless write.closed?
  read.close  unless read.closed?
  Process.kill 'TERM', pid if pid
end

request_test_example.rb

p request_test {|test|
  test.response {|env|
    [200, {'Content-Type' => 'application/json'}, ['Nyan!']]
  }

  test.request {
    puts Net::HTTP.get(test.uri)
  }
}