What does Genesis 42:8 mean?

Joseph's brothers have aged at least two decades since he last saw them. He was seventeen when they sold him as a slave (Genesis 37:2, 28), thirty when he rose to power in Egypt (Genesis 41:46–47, 53–54), and he has governed the nation for more than seven years (Genesis 41:53–54). Had Joseph seen just one of his brothers, he might not have known who he was, at first. But he had the advantage of seeing them all together. These were the faces of his long-lost family; they are also the faces of his betrayers.

The brothers don't recognize Joseph, however. That is no surprise. Not only has he aged from seventeen to nearly forty, but he has also adapted the fashion and appearance of Egyptian royalty, including an Egyptian name, wife, and sons (Genesis 41:42–43, 50–52). He speaks Egyptian (Genesis 42:23).

At first, Joseph chooses to maintain his secret (Genesis 42:7). This is partly to contain his own emotions (Genesis 42:24). It's likely due to a well-justified sense of anger, as well. It is also to allow for the brothers to be tested, as the following chapters explain.