I am not testing you. I think "thu thach" could also mean testing.
“I am not challenging you” is a more natural English translation, I think it should be accepted
Can't change verb tense though.
In what situation would one use the words "thử thách"? Does it have a negative, positive, or neutral connotation?
In a contest, maybe. You can say "tôi muốn thử thách bạn với một vài câu hỏi sau đây" (positive/neutral connotation). It can carry negative connotation but I can't think of one right now.
Owl, Tôi sẽ thử thách bạn mỗi ngày.