Does MainWP have Visual Regression Tests?

MainWP has a Regression Testing add-on.

This feature monitors changes in your child sites’ source code and helps you spot unexpected modifications after plugin, theme, or WordPress core updates. It works by comparing HTML snapshots of a page (by default the homepage, but you can choose a different page) between scans. If the changes exceed a set threshold, you can be notified by email.

You can run scans manually, schedule them (daily, weekly, twice per month, monthly), or trigger them automatically after updates. The add-on provides several ways to review differences, including raw HTML comparisons, rendered before/after views, and even changes in CSS/JS files if tracking is enabled.

For full details on how to use it, please see the Regression Testing help article.