How are you ladies dealing with your bubs testing your boundaries?

My son has recently found it amusing if I say no to him or ask him to stop doing something. He now smiles at me and continues to be defiant. It’s driving me crazy because I feel like I’m constantly battling with him. Like for example I ask him not to play on the stairs, his response is to sit on the stairs and smile at me then go up a step and sit there. I ask him to come down and he won’t listen but sit there smiling. So I physically remove him myself (not rough or anything) and of course he cries and has a tantrum. Or he hits me and I tell him no hitting and he’ll do it again and I’ll say no you don’t hit mommy. He’ll do it again with a smirk and I’ll physically move him away and say no that’s not ok you don’t hit mommy. It’s really getting frustrating. He’s overall a very fun, intelligent, sweet little bubs, but this new testing my boundaries thing s wearing my nerves. I know it’s a normal learning thing blah blah 🙄 but what do you guys do?