What's the best way to test checkout flow changes?

As a Shopify store owner, I've learned the hard way that checkout flow isn't just a technical detail—it's the make-or-break moment for your entire business. Last quarter, I noticed our cart abandonment rate was hovering around 70%, which was killing our conversion rates and wasting precious ad spend. I knew something was wrong, but pinpointing exactly what was challenging. Was it the number of form fields? The payment options? The loading speed? The uncertainty was driving me crazy. I'd heard horror stories of merchants who made sweeping changes without proper testing and saw their conversion rates plummet. I didn't want to be another cautionary tale. My team and I needed a systematic, data-driven approach to understand and optimize our checkout process. We needed to test changes methodically, track every interaction, and make informed decisions—not just gut feelings. The stakes are high: even a 1-2% improvement in checkout conversion can translate to thousands of dollars in additional monthly revenue. But how do you test checkout flow without risking your entire store's performance? What tools and strategies can help me understand exactly where potential customers are dropping off and why?