test_spawn_sh occasionally fails

[kulikjak]

When I started testing ptyprocess with Python 3.11 I found out that test_spawn_sh fails with:

E       AssertionError: assert b'echo $ENV_KEY; exit 0' in b'\rjkulik@kuldavm-sparc-6717:...process/ptyprocess-0.7.0/tests$ echo $ENV \x08_KEY; exit 0\r\nenv_value\r\n'                                                
E        +  where b'echo $ENV_KEY; exit 0' = <built-in method strip of bytes object at 0x1fffc6b2a9f8b0>()                                                                                                              
E        +    where <built-in method strip of bytes object at 0x1fffc6b2a9f8b0> = b'echo $ENV_KEY; exit 0\n'.strip

I did some testing and it seems that this is caused by some kind of a race condition / it's speed dependent. When I run the test suite for the second time, it passes. But then when I delete the __pycache__ directory, it fails again.

I also found out that when I add a sleep after the spawn, it fails every time in every Python (and not just this test, test_spawn_sh_unicode as well):

--- ptyprocess-0.7.0/tests/test_spawn.py
+++ ptyprocess-0.7.0/tests/test_spawn.py
@@ -21,6 +21,7 @@ class PtyTestCase(unittest.TestCase):
     def _spawn_sh(self, ptyp, cmd, outp, env_value):
         # given,
         p = ptyp.spawn(['sh'], env=self.env)
+        time.sleep(1)
         p.write(cmd)

         # exercise,