This new helper is very similar to "test-hashmap.c" and will help
test how `struct oidmap` from oidmap.{c,h} can be used.
Helped-by: SZEDER Gábor <szeder.dev@gmail.com>
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
