So how do I test if my workplace is doing a good job of this? The article mentions badssl.com. Do I just click all the red links in the certificate section and verify that my browser is refusing to display the pages?
You want to do that both on your intercepted LAN and with a direct connection and compare the results. If they both give the same results you can be happy your MitM proxy is at least treating insecure sites equivalently. You still lose the advantage that you browser will tell you why the site is insecure