Test with background thread

Use the test case from puma#1868

Looks like puma#1961 does not test with a
background thread

test/rackup/jruby-sigint.ru

@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+java_import java.util.concurrent.ThreadPoolExecutor
+java_import java.lang.Runnable
+
+# From https://github.com/ruby-concurrency/concurrent-ruby/blob/d11b29c37b81320ca7126cc9cd85f4f3d17a78a3/lib/concurrent/executor/java_thread_pool_executor.rb#L111-L117
+pool = java.util.concurrent.ThreadPoolExecutor.new(
+    2,
+    2,
+    60,
+    java.util.concurrent.TimeUnit::SECONDS,
+    java.util.concurrent.LinkedBlockingQueue.new,
+    java.util.concurrent.ThreadPoolExecutor::AbortPolicy.new
+  )
+
+# From concurrent-ruby: https://github.com/ruby-concurrency/concurrent-ruby/blob/d11b29c37b81320ca7126cc9cd85f4f3d17a78a3/lib/concurrent/executor/java_executor_service.rb#L77-L87
+class Job
+  include Runnable
+  def initialize(args, block)
+    @args = args
+    @block = block
+  end
+
+  def run
+    @block.call(*@args)
+  end
+end
+
+2.times do
+  pool.submit Job.new(nil, proc { sleep })
+end
+
+at_exit do
+  # Request threadpool shutdown.
+  pool.shutdown
+  # Add two seconds wait to let the threads finish and then kill the threads.
+  deadline = Time.now + 2
+  while true
+    break if pool.get_active_count.zero?
+    if Time.now > deadline
+      pool.shutdownNow
+      break
+    end
+  end
+end
+
+run lambda { |env| [200, {"Content-Type" => "text/plain"}, ["Hello World"]] }

test/test_integration_single.rb

@@ -75,7 +75,7 @@ def test_term_not_accepts_new_connections
   def test_int_refuse
     skip_unless_signal_exist? :INT
 
-    cli_server 'test/rackup/hello.ru'
+    cli_server 'test/rackup/jruby-sigint.ru'
     begin
       sock = TCPSocket.new(HOST, @tcp_port)
       sock.close