Perhaps the safeword is really for me as the dom... more than the sub. How can I explore my limits if I am in fear of hurting/damaging my sub?

I need that safeword so I can escalate with confidence.

And that's the point perhaps, of having that occasional session where I say, let's test your limits. So we can see what you the sub does and does not enjoy. Your limits/tolerance may be wildly different from another persons... especially considering one day the test might be about "impact pain" and another day it's about "wax heat" or "compression" or "hogtie" pain.

Shouldn't the test precedes the scene?