add tests

tests/ActivityloggerTest.php

@@ -203,10 +203,24 @@ public function it_will_not_replace_non_placeholders()
         $this->assertEquals($description, $this->getLastActivity()->description);
     }
 
-    public function it_returns_an_instance_of_the_activity_log_after_logging()
+    public function it_returns_an_instance_of_the_activity_after_logging()
     {
         $activityModel = activity()->log('test');
 
         $this->assertInstanceOf(Activity::class, $activityModel);
     }
+
+    /** @test */
+    public function it_returns_an_instance_of_the_activity_log_after_logging_when_using_a_custom_model()
+    {
+        $activityClass = new class extends Activity {};
+
+        $activityClassName = get_class($activityClass);
+
+        $this->app['config']->set('laravel-activitylog.activity_model', $activityClassName);
+
+        $activityModel = activity()->log('test');
+
+        $this->assertInstanceOf($activityClassName, $activityModel);
+    }
 }