PHPStorm Testing: Cannot select phpunit to run test

I am unable to run a directory/folder as a PHPUnit test from the context menu - it offers browser debugging and running as a php script only. I can set one up tests in the "Edit configurations" panel, and they work fine, but I have hundreds of test files, and cannot set each one up individually.

At one point, in a previous project, I could ctrl + t and it would run the file/test I was in as a phpunit test, without any previous configuration for the file. I've reviewed my setup and they look identical.

Settings -> PHPUnit script is set to vendor\autoload, default config file is pointed to local phpunit.xml.

Edit Configurations -> Defaults -> PHPUnit is set to use default configuration file.

Again, I can run phpunit tests, it just seems like my phpstorm is no longer recognising the files as suitable for phpunit unless I specify each one

PhpStorm 2017.1.3

PHPunit 5.7.20

PHP 5.6

Any advice would be appreciated, thanks.