Наследование: extends Stub_Parent_Model, use trait Znck\Eloquent\Traits\BelongsToThrough
 public function test_through_one()
 {
     $district = Stub_Test_Model_District::where('id', 1)->first();
     $this->assertNotNull($district->country);
     $this->assertEquals(1, $district->country->id);
 }
 public function test_custom_foreign_key()
 {
     $district = Stub_Test_Model_District::where('id', 1)->first();
     $this->assertNotNull($district->countryOffshore);
     $this->assertEquals(1, $district->countryOffshore->id);
 }