Clash Royale has two other amazing features that we'd absolutely love to see in Clash of Clans. Being able to fight members of our own clan, or do test battles. It doesn't get players gold, upgrade troops, trophies or anything else. It's more for fun. However, it's that added fun that makes it great. Being able to test different troops, what works best together and more against friends or a training ground, rather than spending 200,000 Elixir in Clash of Clans and hoping it works, then having to wait another 30-45 minutes to brew another army. Yes we can attack the goblin map, but they aren't ideal, or realistic compared to what we face during actual multiplayer attacks.
Clash of Clans could greatly benefit by adding "test-run" battles or letting Clan members fight against each other. It could even help Clan members find weaknesses in a base, and improve the competitiveness overall. Of course it's a much different game and we're attacking entire villages, and the war is one-sided where the enemy doesn't fight back, but it's still one of many things we'd love Clash of Clans to borrow from Clash Royale.