If you're doing this, though, you should turn autosave off, as it could trigger as soon as the battle ends if you knock the shiny out, overwriting your shiny save and denying you a second chance. Pokemon spawns are carried over between saves in this game, meaning a hard save can act as a nice insurance policy. You can save in front of a shiny and reset if you accidentally knock it out, or it struggles. Pokemon refuse to auto-battle shinies (so that they don't accidentally KO these rarities), so if you send your Pokemon out to auto-battle the potential shiny, and it doesn't engage, you know you have a shiny on your hands.
Using the Let's Go feature, where you send out the first Pokemon in your party with the R button, you can aim it at the potential shiny. There is one saving grace, though - if you're unsure if a Pokemon is shiny or not (often the case for subtle shinies, like Pikachu or Tandemaus), there is a way to check without entering into a battle.
There is no indicator of any sort to let you know that a shiny Pokemon has spawned, so you'll need to keep your eyes peeled and have a good look at any wild Pokemon you pass if you're serious about not missing any potential shinies.
