chef stateful shell test randomly fails

[bzbarsky-apple]

Problem

I've now seen a number of failures like https://github.com/project-chip/connectedhomeip/runs/6817356066?check_suite_focus=true in CI. Retriggering the jobs typically makes them pass.

Log says:

FAILED: python/gen/examples/chef/chef.tests.test_stateful_shell.py.pw_pystamp 
python3 ../../third_party/pigweed/repo/pw_build/py/pw_build/python_runner.py --gn-root ../../ --current-path ../../examples/chef --default-toolchain=//build/toolchain/linux:linux_x64_clang --current-toolchain=//third_party/pigweed/repo/pw_build/python_toolchain:python --touch python/gen/examples/chef/chef.tests.test_stateful_shell.py.pw_pystamp --capture-output --lockfile pip.lock -- ../../examples/chef/test_stateful_shell.py
test123
.123
...1234
F
======================================================================
FAIL: test_set_env_outside_shell (__main__.TestStatefulShell)
Tests setting env variables outside shell call.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/__w/connectedhomeip/connectedhomeip/out/clang/../../examples/chef/test_stateful_shell.py", line 33, in test_set_env_outside_shell
    self.assertEqual(resp, "1234")
AssertionError: '' != '1234'
+ 1234
----------------------------------------------------------------------
Ran 5 tests in 0.321s
FAILED (failures=1)

Proposed Solution

Fix the test.

@cpagravel @andy31415

[cpagravel]

Is that the only test of the 5 that are failing?

[cpagravel]

It is not the only one that failed. Here is an example of a different test failing: https://github.com/project-chip/connectedhomeip/runs/6817031289?check_suite_focus=true

I suspect we are reading the file before it has been completely written to. I'll make a PR.

[cpagravel]

I added the fix to the PR #19362 . Unfortunately, the only way to test it is to run it a bunch of times.