A Cultivation Master-Disciple Story: After the Disciple Dies, They Discover the World Is a Novel About an Overpowered Hero, Then Are Reborn 修仙师徒文徒弟死后发现世界是一本龙傲天书，重生

Looking for something like "You Don't Have a Master’s Wife. Right, You Only Have a Martial Uncle". The master has only one disciple and spends most of his time in seclusion. The protagonist, Long Aotian, comes to apply to join the sect. During a trial, his childhood friend dies protecting him. After the trial, while they’re recovering, he finds something in the back mountains...