tmux_cmd(feat[logging]): Add pre-execution command logging

why: tmux_cmd logs stdout after execution and exceptions, but never logs
the command before execution. Pre-execution logging is the prerequisite
for a future dry-run mode in tmuxp (tmuxinator's debug / teamocil's
--debug equivalent).
what:
- Add logger.debug call before subprocess.Popen in tmux_cmd.__init__
- Add test verifying pre-execution log message contains command

Author: tony

src/libtmux/common.py

@@ -259,6 +259,8 @@ def __init__(self, *args: t.Any) -> None:
 
         self.cmd = cmd
 
+        logger.debug("running %s", subprocess.list2cmdline(cmd))
+
         try:
             self.process = subprocess.Popen(
                 cmd,

tests/test_common.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import logging
 import re
 import sys
 import typing as t
@@ -27,6 +28,7 @@
 )
 
 if t.TYPE_CHECKING:
+    from libtmux.server import Server
     from libtmux.session import Session
 
 version_regex = re.compile(r"([0-9]\.[0-9])|(master)")
@@ -508,3 +510,15 @@ def mock_get_version() -> LooseVersion:
     elif check_type == "type_check":
         assert mock_version is not None  # For type checker
         assert isinstance(has_version(mock_version), bool)
+
+
+def test_tmux_cmd_pre_execution_logging(
+    caplog: pytest.LogCaptureFixture,
+    server: Server,
+) -> None:
+    """Verify tmux_cmd logs command before execution."""
+    with caplog.at_level(logging.DEBUG, logger="libtmux.common"):
+        server.cmd("list-sessions")
+    assert any(
+        "running" in r.message and "list-sessions" in r.message for r in caplog.records
+    )