Current, if you want to test strategies or practice on shards you need to use a shard and if you want to test/practice more on it you need to either stack up a bunch of that specific shard or hope you get another one soon.
To make it easier to practice and test different strategies I suggest reusable training shards that you aquire from breaking down a shard.
Basically if you break down a level 7 shard for desert crypt you would get a level 7 training shard for Desert crypt. This could be used as a normal shard, but would either not dissappear once you start it or given back at the end and also wouldn’t give any rewards or item drops.
I’m not asking to get this added in the current game, but hoping that we can get it at some point in reborn.