https://github.com/pytest-dev/pytest-xprocess/issues/154

--- pytest-xprocess-1.0.2/tests/test_process_initialization.py.orig
+++ pytest-xprocess-1.0.2/tests/test_process_initialization.py
@@ -1,5 +1,6 @@
 import socket
 import sys
+import time
 from pathlib import Path
 
 import pytest
@@ -126,6 +127,7 @@
         args = [sys.executable, server_path, tcp_port, "--no-children"]
 
         def startup_check(self):
+            time.sleep(1)
             return request_response_cycle(tcp_port, data)
 
     xprocess.ensure(proc_name, Starter)
@@ -153,6 +155,7 @@
         args = [sys.executable, server_path, tcp_port, "--no-children"]
 
         def startup_check(self):
+            time.sleep(1)
             return request_response_cycle(tcp_port, data)
 
     if proc_name == "s1":