שִׁלְח֨וּ מִכֶּ֣ם אֶחָד֮ וְיִקַּ֣ח אֶת־אֲחִיכֶם֒ וְאַתֶּם֙ הֵאָ֣סְר֔וּ וְיִבָּֽחֲנוּ֙ דִּבְרֵיכֶ֔ם הַֽאֱמֶ֖ת אִתְּכֶ֑ם וְאִם־לֹ֕א חֵ֣י פַרְעֹ֔ה כִּ֥י מְרַגְּלִ֖ים אַתֶּֽם׃
Send one of you, and let him fetch your brother, and ye shall be bound, that your words may be proved, whether there be truth in you; or else, as Pharaoh liveth, surely ye are spies.’
Rashi on Genesis
האמת אתכם means WHETHER THERE BE TRUTH IN YOU — therefore the ה has the vowel Patach, because it is a kind of question. And if you do not (ואם לא) bring) him חי פרעה כי מרגלים אתם BY THE LIFE OF PHARAOH, SURELY YOU ARE SPIES.
Or HaChaim on Genesis
שלחו מכם אחד, "Despatch one of you, etc." They did not do this as they were concerned that their father would worry needlessly about the fate of all the remaining brothers.
Radak on Genesis
if you indeed speak the truth, as you claimed when you said that you are כנים, truthful, above board.