test_pyrepl may read its own output #121603
Description
First, a caveat: I don't understand psuedo-terminals well and I'm fairly confused by this.
When process start-up is slow (such as under heavy load), the pyrepl tests that use test_pyrepl.run_repl may read their own command as output. Data that is written to master_fd is immediately available to be read from mater_fd, so if the subprocess is not quick enough at reading the input.
cpython/Lib/test/test_pyrepl/test_pyrepl.py
Line 933 in ef10110
cpython/Lib/test/test_pyrepl/test_pyrepl.py
Lines 948 to 952 in ef10110
This leads to test errors that look like:
FAIL: test_python_basic_repl (test.test_pyrepl.test_pyrepl.TestMain.test_python_basic_repl)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/raid/sgross/cpython/Lib/test/support/__init__.py", line 2622, in wrapper
return func(*args, **kwargs)
File "/raid/sgross/cpython/Lib/test/test_pyrepl/test_pyrepl.py", line 892, in test_python_basic_repl
self.assertIn("True", output)
~~~~~~~~~~~~~^^^^^^^^^^^^^^^^
AssertionError: 'True' not found in 'from test.support import initialized_with_pyrepl\r\ninitialized_with_pyrepl()\r\nexit()\r\n'
In other words, the parent is seeing its own command as if its the output from the subprocess.