fix: correct PermissionError handling in is_process_alive, add corrupt PID test

tests/unit/test_process.py

@@ -1,11 +1,9 @@
 import os
 import pytest
 from datetime import datetime, timezone, timedelta
-from unittest.mock import patch
 from autossh_mgr.process import (
     write_pid_file, read_pid_file, delete_pid_file,
     is_process_alive, check_stale, get_status, format_uptime,
-    TunnelStatus,
 )
 
 
@@ -95,3 +93,11 @@ def test_format_uptime_hours():
 def test_format_uptime_days():
     started = datetime.now(timezone.utc) - timedelta(days=1, hours=5)
     assert format_uptime(started) == "1d 5h"
+
+
+def test_read_pid_file_corrupt(config_dir):
+    import click
+    pid_path = config_dir / "pids" / "web-service.pid"
+    pid_path.write_text("only-one-line\n")
+    with pytest.raises(click.ClickException, match="Corrupt PID file"):
+        read_pid_file(config_dir, "web-service")