Add a set of tests for subcmd routines. Currently it fails the last one
since there's a bug. It'll be fixed by the next commit.
$ perf test subcmd
69: libsubcmd help tests :
69.1: Load subcmd names : Ok
69.2: Uniquify subcmd names : Ok
69.3: Exclude duplicate subcmd names : FAILED!
Reviewed-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250701201027.1171561-2-namhyung@kernel.org
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
