Prophet Yusuf (Joseph) - Joseph's Plan

The brothers left enough provisions behind for Judah, who stayed at a tavern awaiting the fate of Benjamin. In the meantime, Joseph kept Benjamin in his house as his personal guest and told him how he had devised the plot to put the king's cup in his bag, in order to keep him behind, so as to protect him. He was also glad that Judah had stayed behind, as he was a good-hearted brother. Joseph secretly arranged to watch over Judah's well-being.

Joseph's plan in sending the others back was to test their sincerity, to see if they would come back for the two brothers they had left behind.

The Brothers Confront Jacob
When they arrived home, they entered upon their father, calling: "0 our father! Your son has stolen!"
He was puzzled, scarcely believing the news. He was overwhelmed with sorrow and his eyes wept tears. "Patience be with me; perhaps Allah will return all of them to me. He is Most Knowing, Most Wise." A pall of lonesomeness closed over him, yet he found consolation in patience and trusted in Allah.

The Brothers Confront Jacob - Qur'anic
Allah revealed to us what happened at their meeting with their father: Judah said: "Return to your father and say: '0 our father! Verily, your son (Benjamin) has stolen, and we testify not except according to what we know, and we could not know the unseen! And ask (the people of) the town where we have been, and the caravan in which we returned and indeed we are telling the truth.
He (Jacob) said: "Nay, but your ownselves have beguiled you into something. So patience is most fitting (for me). May be Allah will bring them (back) all to me. Truly He! Only He is All-Knowing, All-Wise."
And he turned away from them and said: "Alas, my grief for Joseph!" And he lost his sight because of the sorrow that he was suppressing. Surah 12: 81-84