ἐξεταστέον
From LSJ
ἀμήχανον δὲ παντὸς ἀνδρὸς ἐκμαθεῖν ψυχήν τε καὶ φρόνημα καὶ γνώμην, πρὶν ἂν ἀρχαῖς τε καὶ νόμοισιν ἐντριβὴς φανῇ → hard it is to learn the mind of any mortal or the heart, 'till he be tried in chief authority | it is impossible to know fully any man's character, will, or judgment, until he has been proved by the test of rule and law-giving
English (LSJ)
A one must scrutinize, Pl.R.599a, Gal.1.357; one must examine carefully, ὅπως . . Jul.Or.7.226d.
Greek (Liddell-Scott)
ἐξεταστέον: ῥημ. ἐπίθ. τοῦ ἐξετάζω, δεῖ ἐξετάζειν, Πλάτ. Πολ. 599Α.