My reporting manager does the coding work too. Both of us coordinate and complete the task. While unit testing, I found that there is a typo in his code. It had to be table A instead of A1. I informed him the same, he corrected it. But, with his body language, I could sense that he was quite offended. And since that day, he has been throwing very sarcastic comments at me, albeit indirectly. Now, how should I deal with this?
I wouldn't bother trying to resolve this. Your boss is immature, so your expectations of change should be low enough that it's not worth the trouble. The whole point of unit tests is to find problems. Unit tests are also completely impersonal and impartial. It makes no sense to get mad at them, or to get mad at the messenger for reporting the findings. If this is how your boss responds to a machine pointing out a simple mistake that is trivial to fix, I would expect a worse reaction to an actual person (and subordinate) pointing out a far more difficult thing to fix.
On the other hand, you didn't say exactly how you informed him of what the unit tests found. If it was in a highly public fashion (at a standup meeting, for instance, or on an email to the whole team), it might have been embarrassing to him and that is why he is reacting the way he is. It's still immature on his part, but perhaps that could be a lesson for you in the future: don't embarrass the boss.
You're in the 1st phase of conflict escalation.
Escalation is charted in five phases, each having its own characteristics and triggers. Stage One is part of normal, everyday life. Even good relationships have moments of conflict. These can only be resolved with great care and mutual empathy. In this stage, people look for objective solutions a cooperative manner. If a solution is not found, especially because one of the parties sticks obstinately to his or her point of view, the conflict escalates.
You should talk to him "under 4 eyes" and tell him that you feel a difference in your relationship since that event. Make sure that you only talk about your impression. Ask him how he feels about that.
I agree with the poster above. It would be beneficial to bring a neutral 3rd party in to talk about it. Explain your side and allow him to respond. Reiterate that you weren't trying to make him look incompetent, you were just "proofreading" as you would with anyone else.