A test model that uses a custom suffix generation method.
Inheritance: extends Cviebrock\EloquentSluggable\Tests\Models\Post
 /**
  * Test that an empty slug source creates a null slug.
  *
  * @test
  */
 public function testEmptySourceGeneratesEmptySlug()
 {
     $post = PostWithCustomSource::create(['title' => 'My Test Post']);
     $this->assertEquals(null, $post->slug);
 }