phpunit testing routes only available after login

I need to create unit tests for controllers / routes that are only accessible for logged in users. I am using IonAuth.

PHP Code:

public function testValidateField()
{
    $route = route_to('invoice_validate_field', 'name');
    $getArray = ['name' => 'Name Surname'];
    $result = $this->call('get', $route, $getArray);
    $this->assertTrue($result->isOK());
    $result->assertRedirectTo('login');
} 


This works, but, as you can see, I can only check if the route gets redirected, because the route is only available for logged in users.

I am using IonAuth for authentication. The login check is performed by a filter.

How do I imitate logged in user in this case? How do I log in?

I see Shield has AuthenticationTesting trait for that. But how do I deal with IonAuth here? Maybe @benedmunds could suggest something?

==

Donatas G.