Add tests for custom job class in worker

tests/test_worker.py

@@ -347,6 +347,22 @@ class TestWorker(RQTestCase):
         worker = Worker([q], job_class=CustomJob)
         self.assertEqual(worker.job_class, CustomJob)
 
+    def test_custom_job_class_by_string(self):
+        """Ensure Worker accepts custom job class using dotted notation."""
+        q = Queue()
+        worker = Worker([q], job_class='test_worker.CustomJob')
+        self.assertEqual(worker.job_class, CustomJob)
+
+    def test_custom_job_class_is_not_global(self):
+        """Ensure Worker custom job class is not global."""
+        q = Queue()
+        worker_custom = Worker([q], job_class=CustomJob)
+        q_generic = Queue()
+        worker_generic = Worker([q_generic])
+        self.assertEqual(worker_custom.job_class, CustomJob)
+        self.assertEqual(worker_generic.job_class, Job)
+        self.assertEqual(Worker.job_class, Job)
+
     def test_work_via_simpleworker(self):
         """Worker processes work, with forking disabled,
         then returns."""