Testing with session

Hello,

I'm trying to test an "Auth" library I created. Obviously, that library uses the session.

My first test looks like this:

PHP Code:

public function testConstructor()
{
    $auth = new Auth();
    $this->assertInstanceOf(\App\Libraries\Auth\Auth::class, $auth);
    $this->assertNull(service('session')->get('user'));
} 


See the line where I ask if $_SESSION['user'] does not exist? That line produces an error:

Code:

ErrorException: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time

If I understand it correctly, that means "session_start()" hasn't been called before the first "echo".

I see two possibilities:

• Call session_start() myself, although I don't know where (in setUp() is also too late).
  
• Use mocks. I saw a "Mocking Services" chapter in the userguide, but I didn't understand how to use it.
  

Which is the correct solution? What are the best practices? and how do I do that?

Thanks in advance!