subcommand: Add tests.

Change-Id: I730f364f30b0d211c2db6da0d6bb4f5ff3c948da
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1999280
Reviewed-by: Anthony Polito <apolito@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
diff --git a/subcommand.py b/subcommand.py
index 08f742b..c4209e6 100644
--- a/subcommand.py
+++ b/subcommand.py
@@ -70,7 +70,7 @@
   # wanted.
   if not any(i in ('-h', '--help') for i in args):
     args = args + ['--help']
-  _, args = parser.parse_args(args)
+  parser.parse_args(args)
   # Never gets there.
   assert False