A.T. Robertson Commentary 1 Thessalonians 3:5

"For this cause I also, when I could no longer forbear, sent that I might know your faith, lest by any means the tempter had tempted you, and our labor should be in vain." — 1 Thessalonians 3:5 (ASV)

That I might know (εις το γνωνα). Paul's common idiom (verse 2), εις το and the infinitive of purpose (second aorist ingressive active of γινωσκω, come to know).

Lest by any means the tempter had tempted you (μη πως επειρασεν υμας ο πειραζων). Findlay takes this as a question with negative answer, but most likely negative final clause with μη πως about a past action with aorist indicative according to the classic idiom as in Ga 2:2 (μη πωσ--εδραμον) and Ga 4:11 after verb of fearing (Robertson, Grammar, p. 988). It is a fear that the thing may turn out to be so about the past.

Should be (γενητα). Here the usual construction appears (aorist subjunctive with μη πως) about the future.