Genesis 44:16
And Judah said, What shall we say unto my lord? what shall we speak? or how shall we clear ourselves? God hath found out the iniquity of thy servants: behold, we are my lord’s servants, both we, and he also with whom the cup is found. And Judah said, What shall we say unto my lord? what shall we speak? or how shall we clear ourselves? God hath found out the iniquity of thy servants: behold, we are my lord’s servants, both we, and he also with whom the cup is found.
Judah speaks for his brothers fallen to the ground before Joseph in his house after the cup is found in Benjamin's sack, admitting they have nothing to say and no way to clear themselves. The iniquity he says God has exposed is their past sin of selling Joseph into Egypt. That confession concerns that past wrong against Joseph, not merely the missing cup.
They understand their present danger of slavery as God allowing their past wrongdoing to return upon them by permitting them to become slaves also. They make no attempt to deny responsibility, offer no defense, or seek to clear themselves. They accept being made servants, all of them together including Benjamin with whom the cup was found.
Joseph's test and his question about divining were meant to bring out remorse by drawing forth acknowledgment of that past wrong so their true feelings would be more fully revealed. Joseph claimed no power of divination, but he was willing for his brothers to believe he could read the secret acts of their lives.