tests/python: improve reporting when a command fails (#6718)

* represent the command accurately using shell quoting;
* show the exit code;
* show both stdout and stderr.

tests/python/shared/fixtures/init.py

@@ -4,6 +4,7 @@
 
 import logging
 import os
+import shlex
 from enum import Enum
 from http import HTTPStatus
 from pathlib import Path
@@ -103,12 +104,13 @@ def _run(command, capture_output=True):
  proc = run(_command) # nosec
  return stdout, stderr
  except CalledProcessError as exc:
- stderr = exc.stderr.decode() or exc.stdout.decode() if capture_output else "see above"
- pytest.exit(
- f"Command failed: {command}.\n"
- f"Error message: {stderr}.\n"
- "Add `-s` option to see more details"
- )
+ message = f"Command failed: {' '.join(map(shlex.quote, _command))}."
+ message += f"\nExit code: {exc.returncode}"
+ if capture_output:
+ message += f"\nStandard output:\n{exc.stdout.decode()}"
+ message += f"\nStandard error:\n{exc.stderr.decode()}"
+
+ pytest.exit(message)
 
 
 def _kube_get_server_pod_name():