Invoke next() on wrapped legacy scheduler

esrally/driver/scheduler.py

@@ -196,7 +196,7 @@ def __init__(self, task, legacy_scheduler_class):
         self.legacy_scheduler = legacy_scheduler_class(task.params)
 
     def next(self, current):
-        return self.legacy_scheduler(current)
+        return self.legacy_scheduler.next(current)
 
 
 class Unthrottled(Scheduler):

tests/driver/scheduler_test.py

@@ -144,3 +144,32 @@ def test_is_simple_scheduler(self):
 
     def test_is_not_simple_scheduler(self):
         self.assertFalse(scheduler.is_simple_scheduler(scheduler.UnitAwareScheduler))
+
+
+class LegacyWrappingSchedulerTests(TestCase):
+    class SimpleLegacyScheduler:
+        # pylint: disable=unused-variable
+        def __init__(self, params):
+            pass
+
+        def next(self, current):
+            return current
+
+    def setUp(self):
+        scheduler.register_scheduler("simple", LegacyWrappingSchedulerTests.SimpleLegacyScheduler)
+
+    def tearDown(self):
+        scheduler.remove_scheduler("simple")
+
+    def test_legacy_scheduler(self):
+        task = track.Task(name="raw-request",
+                          operation=track.Operation(
+                              name="raw",
+                              operation_type=track.OperationType.RawRequest.name),
+                          clients=1,
+                          schedule="simple")
+
+        s = scheduler.scheduler_for(task)
+
+        self.assertEqual(0, s.next(0))
+        self.assertEqual(0, s.next(0))