added a test for the race condition

tests/test_worker.py

@@ -11,6 +11,8 @@ import time
 from multiprocessing import Process
 import subprocess
 
+import mock
+
 from tests import RQTestCase, slow
 from tests.fixtures import (create_file, create_file_after_timeout,
                             div_by_zero, do_nothing, say_hello, say_pid,
@@ -567,6 +569,40 @@ class TestWorker(RQTestCase):
         worker.work(burst=True)
         self.assertEqual(self.testconn.zcard(registry.key), 0)
 
+    def test_job_dependency_race_condition(self):
+        """Dependencies added while the job gets finished shouldn't get lost."""
+
+        # This patches the enqueue_dependents to enqueue a new dependency AFTER
+        # the original code was executed.
+        orig_enqueue_dependents = Queue.enqueue_dependents
+
+        def new_enqueue_dependents(self, job, *args, **kwargs):
+            orig_enqueue_dependents(self, job, *args, **kwargs)
+            if hasattr(Queue, '_add_enqueue') and Queue._add_enqueue.id == job.id:
+                Queue._add_enqueue = None
+                Queue().enqueue_call(say_hello, depends_on=job)
+
+        Queue.enqueue_dependents = new_enqueue_dependents
+
+        q = Queue()
+        w = Worker([q])
+        with mock.patch.object(Worker, 'execute_job', wraps=w.execute_job) as mocked:
+            parent_job = q.enqueue(say_hello, result_ttl=0)
+            Queue._add_enqueue = parent_job
+            job = q.enqueue_call(say_hello, depends_on=parent_job)
+            w.work(burst=True)
+            job = Job.fetch(job.id)
+            self.assertEqual(job.get_status(), JobStatus.FINISHED)
+
+            # The created spy checks two issues:
+            # * before the fix of #739, 2 of the 3 jobs where executed due
+            #   to the race condition
+            # * during the development another issue was fixed:
+            #   due to a missing pipeline usage in Queue.enqueue_job, the job
+            #   which was enqueued before the "rollback" was executed twice.
+            #   So before that fix the call count was 4 instead of 3
+            self.assertEqual(mocked.call_count, 3)
+
 
 def kill_worker(pid, double_kill):
     # wait for the worker to be started over on the main process