I downloaded a whole WP install and moved it to a LAMP test environment in order to update it. The original site could be found under example.com, the test site should be under example.com.mytestdomain.com aka {testurl}.

I can access {testurl}/wp-admin fine, and both the site address as well as the home address are set to {testurl}, and not example.com.

Yet, when I try to access {testurl}, I am always being forwarded to example.com.

I'd be grateful for hints why this could be happening. I have no redirect plugins, (internal) DNS is set up correctly.