How to Validate Demand for a New ICP Before Launching an Outbound Campaign

Hey everyone, need some input on ICP validation. Context: I run outbound for a custom software development client. Our current campaign targets a very specific niche in US health tech, built around regulatory and certification signals, and that logic works because the signal itself tells us who has the problem right now. Now I want to open a second ICP, most likely custom ERP development for mid-market companies, but I keep going back and forth on it. My problem is not finding companies, it is knowing whether there is enough real demand in an industry before I spend weeks building lists and infrastructure around it. So my question for people who have launched campaigns into a new industry: how do you actually measure demand for a new ICP before committing? Do you look at hiring data, tool adoption, funding activity, community chatter, or do you just run a small 200-300 lead test campaign and let reply data decide? Would love to hear how you approach this or swap notes if you have been through the same thing. Thanks in advance.