Realtime facade with constructor in Test

Hi,

I have a class like this, where I can override an email when I need to in the constructor:

class MyClass
{

    protected $email;

    public function __construct($email = null)
    {
        $this->email = (null == $email) ? \Auth::user()->email : $email;
    }

    public function foo()
    {
        return 'bar';
    }

}

Now in my tests I want to leverage the realtime Facades. So this is what it looks like:

use  Facades\App\Services\MyClass;

class WhateverTest extends TestCase
{
    /** @test */
    public function it_tests_something()
    {
        MyClass::shouldReceive('foo')->andReturn('this is a test');
    }
}

My problem now is the constructor in the MyClass. How can I put an email in the constructor? Hope someone can help me!