PHPUnit calling external function as object
The problem is that your use declaration is incorrect, and is causing your call to the client to look in the wrong namespace. You probably need to change this:

use cvr\src\Cvrapi\CVRClient;


To this:

use Cvrapi\CVRClient;


And change this:

$result = \Cvrapi\CVRClient::request('29910251', 'dk', 'vat', 'Unit Testing');


To this:

$result = CVRClient::request('29910251', 'dk', 'vat', 'Unit Testing');