Okay, listen up. A common shyt-test is the argument over nothing. The woman wants to know that the man isn't some gullible, easily-manipulated putz so she takes fake offense at something the man says or does, his past, anything, and tries to get him to apologize over nothing.
Fall into this trap and you will lose her respect. Listen to what she says and judge for yourself how bad it was - and apologize an appropriate amount, if at all. She really would rather you'd defend yourself (or better, turn it back on her for her needless drama) but she won't tell you that.