Q: How do I actually TEST that my redirects are correct, not just that they exist?

Q: How do I actually TEST that my redirects are correct, not just that they exist?

Great distinction. 'It redirects somewhere' and 'it redirects correctly' are very different. Here's how to verify properly.

Short answer: check status code, hop count, and destination for every old URL — at scale.

Long answer:
— Put your full old-URL list into Screaming Frog in list mode.
— Run it and check three columns: Status Code (want 301), Redirect URL (want the right destination), and Number of Redirects (want 1).
— Sort for anything that's 302, 307, 404, or 200-without-redirect.
— Filter for chains (more than one hop) and loops.
— Manually click 15 to 20 high-value URLs in a browser to confirm the landing page is the right content, not just the right status.

Next step: anything not a clean single 301 to the correct page goes on a fix list, sorted by traffic and backlinks first.