I felt a small pop in my left chest the other day during pushups. the hole in the left chest muscle appears different from the right. there is mild discomfort and no bruising or swelling. could this be a pec tear?

If you do not see any swelling and bruising and you are still able to move your left arm freely, pectoralis tear is very less likely.

Sounds like you may have experienced a mild joint "pop" at articulating contact (like popping you finger joints). Alternatively, you might have a minor muscular strain. If you are taking "muscle building" steroids, however, you need to know that muscular ruptures can occur in that scenario.