diff --git a/airflow/jobs.py b/airflow/jobs.py
index 39e3462faae664..00d4864b1d3a99 100644
--- a/airflow/jobs.py
+++ b/airflow/jobs.py
@@ -168,15 +168,17 @@ def heartbeat(self):
             if job.state == State.SHUTDOWN:
                 self.kill()
 
-            # Figure out how long to sleep for
-            sleep_for = 0
-            if job.latest_heartbeat:
-                sleep_for = max(
-                    0,
-                    self.heartrate - (timezone.utcnow() -
-                                      job.latest_heartbeat).total_seconds())
-
-            sleep(sleep_for)
+            is_unit_test = conf.getboolean('core', 'unit_test_mode')
+            if not is_unit_test:
+                # Figure out how long to sleep for
+                sleep_for = 0
+                if job.latest_heartbeat:
+                    seconds_remaining = self.heartrate - \
+                        (timezone.utcnow() - job.latest_heartbeat)\
+                        .total_seconds()
+                    sleep_for = max(0, seconds_remaining)
+
+                sleep(sleep_for)
 
             # Update last heartbeat time
             with create_session() as session:
diff --git a/tests/test_jobs.py b/tests/test_jobs.py
index 42046d2fbb5f16..e16c9d9a0a7f89 100644
--- a/tests/test_jobs.py
+++ b/tests/test_jobs.py
@@ -133,6 +133,11 @@ def abort():
 class BackfillJobTest(unittest.TestCase):
 
     def setUp(self):
+        with create_session() as session:
+            session.query(models.DagRun).delete()
+            session.query(models.Pool).delete()
+            session.query(models.TaskInstance).delete()
+
         self.parser = cli.CLIFactory.get_parser()
         self.dagbag = DagBag(include_examples=True)
 
@@ -1207,7 +1212,7 @@ def test_backfill_run_backwards(self):
         job = BackfillJob(
             dag=dag,
             start_date=DEFAULT_DATE,
-            end_date=DEFAULT_DATE + datetime.timedelta(days=5),
+            end_date=DEFAULT_DATE + datetime.timedelta(days=1),
             run_backwards=True
         )
         job.run()