xvfb.py complains if command points to a directory.

testing/xvfb.py

 #!/usr/bin/env python
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Runs tests with Xvfb and Openbox on Linux and normally on other platforms."""
 
 import os
+import os.path
 import platform
 import signal
 import subprocess
 import sys
 import threading
 
 import test_env
 
 
 def _kill(proc, send_signal):
@@ skipping 54 matching lines @@
       if xvfb_script.endswith('.pyc'):
         xvfb_script = xvfb_script[:-1]
       return subprocess.call(['xvfb-run', '-a', "--server-args=-screen 0 "
                               "1280x800x24 -ac -nolisten tcp -dpi 96",
                               xvfb_script] + cmd, env=env)
   else:
     return test_env.run_executable(cmd, env)
 
 
 def main():
+  USAGE = 'Usage: xvfb.py [command args...]'
   if len(sys.argv) < 2:
+    print >> sys.stderr, USAGE
+    return 2
+  if os.path.isdir(sys.argv[1]):

[Tom Anderson, 2017/03/14 22:43:43]

nit: add a comment explaining why we have this case

[carlosk, 2017/03/14 23:47:23]

Done.

     print >> sys.stderr, (
-        'Usage: xvfb.py [command args...]')
-    return 2
+        'Invalid command: it\'s a directory')
+    print >> sys.stderr, USAGE
+    return 3
   return run_executable(sys.argv[1:], os.environ.copy())
 
 
 if __name__ == "__main__":
   sys.exit(main())