[tests] When test_venv.test_with_pip() fails, a bug in error handling fails to display stderr

[vstinner]

https://buildbot.python.org/all/#/builders/719/builds/1696

ERROR: test_with_pip (test.test_venv.EnsurePipTest.test_with_pip)
----------------------------------------------------------------------
Traceback (most recent call last):
 File "/buildbot/buildarea/3.x.pablogsal-arch-x86_64.clang-ubsan/build/Lib/test/test_venv.py", line 660, in nicer_error
 yield
 File "/buildbot/buildarea/3.x.pablogsal-arch-x86_64.clang-ubsan/build/Lib/test/test_venv.py", line 595, in do_test_with_pip
 self.run_with_capture(venv.create, self.env_dir,
 File "/buildbot/buildarea/3.x.pablogsal-arch-x86_64.clang-ubsan/build/Lib/test/test_venv.py", line 87, in run_with_capture
 func(*args, **kwargs)
 File "/buildbot/buildarea/3.x.pablogsal-arch-x86_64.clang-ubsan/build/Lib/venv/__init__.py", line 459, in create
 builder.create(env_dir)
 File "/buildbot/buildarea/3.x.pablogsal-arch-x86_64.clang-ubsan/build/Lib/venv/__init__.py", line 76, in create
 self._setup_pip(context)
 File "/buildbot/buildarea/3.x.pablogsal-arch-x86_64.clang-ubsan/build/Lib/venv/__init__.py", line 349, in _setup_pip
 subprocess.check_output(cmd, stderr=subprocess.STDOUT)
 File "/buildbot/buildarea/3.x.pablogsal-arch-x86_64.clang-ubsan/build/Lib/subprocess.py", line 465, in check_output
 return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "/buildbot/buildarea/3.x.pablogsal-arch-x86_64.clang-ubsan/build/Lib/subprocess.py", line 569, in run
 raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '['/tmp/test_python_92rnuaxl/tmpkaiesc24/bin/python', '-Im', 'ensurepip', '--upgrade', '--default-pip']' returned non-zero exit status 1.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
 File "/buildbot/buildarea/3.x.pablogsal-arch-x86_64.clang-ubsan/build/Lib/test/test_venv.py", line 672, in test_with_pip
 self.do_test_with_pip(False)
 File "/buildbot/buildarea/3.x.pablogsal-arch-x86_64.clang-ubsan/build/Lib/test/test_venv.py", line 594, in do_test_with_pip
 with self.nicer_error():
 File "/buildbot/buildarea/3.x.pablogsal-arch-x86_64.clang-ubsan/build/Lib/contextlib.py", line 155, in __exit__
 self.gen.throw(value)
 File "/buildbot/buildarea/3.x.pablogsal-arch-x86_64.clang-ubsan/build/Lib/test/test_venv.py", line 663, in nicer_error
 err = exc.stderr.decode(errors="replace")
 ^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'decode'

[dorosch]

Hello @vstinner
Looks like this has been fixed in #98263

[vstinner]

Cool! I close my issue.