It is what I said to you; you are spies
"like I already said, you are spies." See how you translated "spies" in Genesis 42:9.
By this you will be tested
This can be stated in active form. AT: "This is how I will test you" (See: rc://en/ta/man/translate/figs-activepassive)
By the life of Pharaoh
This phrase indicates a solemn oath. AT: "I swear by the life of Pharaoh"
Send one of yourselves and let him get your brother
"Choose one of you to go get your brother"
You will remain in prison
"The rest of you will remain in prison"
that your words may be tested, whether there is truth in you
This can be stated in active form. AT: "so that I may find out if you are telling the truth" (See: rc://en/ta/man/translate/figs-activepassive)