By this you shall be tested: this points to the test the brothers will be put through. Joseph may suspect that the brothers have done away with Benjamin the same as they did with him. We may translate, for example, “You will now be given a chance to prove that what you say is true,” “I am going to put you to the test on this,” or “… to see if what you say about your younger brother is true.”

By the life of Pharaoh: Joseph is using this expression as an oath. According to Driver this kind of oath is found on Egyptian monuments. It is equivalent to the Hebrew oath “As the LORD lives” and “As your soul lives” in 1 Sam 14.39 and 17.55. Translators should refer to similar cases of swearing an oath in 14.22 and 21.23-24. To swear by the life of the king was to affirm by the highest authority under God that what Joseph said would really happen. The literal expression of the oath may need to be adjusted in translation to say, for example, “By the power of Pharaoh” or “As sure as the king is alive and well.” See Good News Translation.

We may translate verse 15, for example, “I swear by the power of the king of Egypt that you [plural] will never leave until your younger brother is brought here.”

Quoted with permission from Reyburn, William D. and Fry, Euan McG. A Handbook on Genesis. (UBS Helps for Translators). New York: UBS, 1997. For this and other handbooks for translators see here .