RossMitchell on "Test environment runs new WordPress site rather than existing site"

Curious about a few things in your setup.
-

copied the existing site into Visual Studio

So you are using VS as project manager, file editor etc.
- Yes you have MySQL, but what is your web server ?
- You don't mention transferring your database. All of your website content is in the database, the files largely serve to display the database contents.
-

"No directory mapping established"

this error would be from your website server, you need to followup this in its documentation.