test: MCP PID lock tests

Part of #734

tests/test_mcp_pid_lock.py

@@ -0,0 +1,75 @@
+"""Tests for MCP PID file lock (#734)."""
+
+import os
+import sys
+import tempfile
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).parent.parent))
+
+# Override MCP_DIR for testing
+import tools.mcp_pid_lock as lock_mod
+_test_dir = Path(tempfile.mkdtemp())
+lock_mod._MCP_DIR = _test_dir
+
+
+def test_acquire_and_release():
+    """Lock can be acquired and released."""
+    pid = lock_mod.acquire_lock("test_server")
+    assert pid == os.getpid()
+    assert lock_mod.is_locked("test_server")
+    lock_mod.release_lock("test_server")
+    assert not lock_mod.is_locked("test_server")
+
+
+def test_concurrent_lock_blocked():
+    """Second acquire returns None when server running."""
+    lock_mod.acquire_lock("test_concurrent")
+    result = lock_mod.acquire_lock("test_concurrent")
+    assert result is None
+    lock_mod.release_lock("test_concurrent")
+
+
+def test_stale_lock_cleaned():
+    """Stale PID files are cleaned up."""
+    # Write a fake stale PID
+    pid_file = _test_dir / "stale.pid"
+    pid_file.write_text("99999999")
+    assert not lock_mod.is_locked("stale")
+    assert not pid_file.exists()
+
+
+def test_list_locks():
+    """list_locks returns only active locks."""
+    lock_mod.acquire_lock("list_test")
+    locks = lock_mod.list_locks()
+    assert "list_test" in locks
+    assert locks["list_test"] == os.getpid()
+    lock_mod.release_lock("list_test")
+
+
+def test_cleanup_stale():
+    """cleanup_stale_locks removes dead PID files."""
+    (_test_dir / "dead1.pid").write_text("99999998")
+    (_test_dir / "dead2.pid").write_text("99999999")
+    count = lock_mod.cleanup_stale_locks()
+    assert count >= 2
+
+
+def test_force_release():
+    """force_release kills process and removes lock."""
+    lock_mod.acquire_lock("force_test")
+    assert lock_mod.is_locked("force_test")
+    lock_mod.force_release("force_test")
+    assert not lock_mod.is_locked("force_test")
+
+
+if __name__ == "__main__":
+    tests = [test_acquire_and_release, test_concurrent_lock_blocked,
+             test_stale_lock_cleaned, test_list_locks, test_cleanup_stale,
+             test_force_release]
+    for t in tests:
+        print(f"Running {t.__name__}...")
+        t()
+        print("  PASS")
+    print("\nAll tests passed.")