system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] If Yoda didn’t think/want Luke to know Darth Vader was his father, why did he tell him facing Vader was his last test to become a Jedi?

As opposed to say, defeating the Emperor. Did Yoda think he would kill Vader without eve knowing he was his father?
gpt
Vader was a greater source of anxiety/fear for Luke (even before Luke knew the secret) so he represented the grand mountain that Luke needed to overcome to be in control of himself. 

Side-note, but Luke's choice to forgive and spare his dad is a grand departure from what Yoda/Ben had in mind, so that could be a seen as a sign that Luke's Jedi Philosophy was already on its way to being better than the Prequel Era Jedi.