Restrict FTP access to a folder that contains php scripts

I have the following files:

/domain/domainname/public_html/index.php

/domain/domainname/tests/test1.php

/domain/domainname/tests/test2.php

/domain/domainname/tests/test3.php

index.php calls test1.php, test2.php, and test3.php

The web host provides FTP access to /domain/domainname which cannot be disabled.

I want index.php to be able to call those three php scripts within tests while blocking FTP access to tests. How do I accomplish this?