The problem is that your use declaration is conflicting with your call to the client in the code. 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');

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');