Since the context relates to prophesyings, the bible is full of prophecies, so it applies. The application is: How strong is your faith? Are you willing to challenge what you claim to believe?
I find some applications of scripture that are marketed as "just reading scripture, so you're disagreeing with God" are actually applied in harmful ways and we are to abstain from even the appearance of evil.
Well, the context verse before the testing verse is about prophesying, and the verse after is saying to abstain from evil, which can require testing what is good and what to abstain from. So, I would say the verse saying to test can mean testing prophesy and all things.
Also, even if this scripture were really restricted to testing prophesy, still it can give me a more general principle > it it is good to test prophesies, then it can be good to test everything else, too. Test what you are thinking, like you would test a prophesy, for example
I think, by the way, of how the Jewish leaders did not make sure with God about how evidence was being presented > they did not seek God's counsel, but judged by how things were made to look > Joshua chapter 9.
Am I willing to challenge what I believe? I can do what God guides me to do > test about what He wants me to test, and how to test. And trust Him about what He really wants me to do. Test Him, by trusting Him, in prayer and submission to what He has me doing.
And "the appearance of evil" can be understood in more than one way. A legalistic way to "abstain from any appearance of evil" could be to stay clear of what wrong people consider to be what looks bad. But just because something looks bad to someone, this does not mean it is really evil making an appearance.
And you could have a politician who is making such a good show that everyone is convinced he or she is a very good person. But in case the person is fooling everybody, then evil is making an appearance!!
So, I would say God is the One who knows, and we can make sure with Him; test with Him
What does He think of my faith, then????