Laravel 5.1 - Eloquent Relationships

I am new to Laravel. I was looking at the Eloquent relationships. I followed the documentation and defined my one to many relationship as:

// in the test model
 public function questions()
   {
      return $this->hasMany('App\Question', 'test_name_id', 'test_id');
   }
// in the question model
public function test()
   {
      return $this->belongsTo('App\Test', 'test_name_id', 'test_id');
   }

Note that i have not followed the convention for naming the id's. So if I do this in the Tinker:

$test = App\Test::first();
$question = $test->questions;

It works fine. But if want the record any other than first like doing:

$test = App\Test::where(['test_id'=>'2'])->get();
$question = $test->questions;

It gives me this error:

PHP error:  Trying to get property of non-object on line 1

Can any one please explain me what I am doing wrong here and how does this work properly?

via Chebli Mohamed