Keep track of previous started event ID

Closes #2107

Signed-off-by: Laurie O <laurie_opperman@hotmail.com>

tests/test_swf/models/test_decision_task.py

@@ -30,9 +30,10 @@ def test_decision_task_full_dict_representation():
     fd["workflowExecution"].should.equal(wfe.to_short_dict())
     fd["workflowType"].should.equal(wft.to_short_dict())
 
-    dt.start(1234)
+    dt.start(1234, 1230)
     fd = dt.to_full_dict()
     fd["startedEventId"].should.equal(1234)
+    fd["previousStartedEventId"].should.equal(1230)
 
 
 def test_decision_task_first_timeout():

tests/test_swf/responses/test_decision_tasks.py

@@ -30,6 +30,30 @@ def test_poll_for_decision_task_when_one():
     )
 
 
+@mock_swf_deprecated
+def test_poll_for_decision_task_previous_started_event_id():
+    conn = setup_workflow()
+
+    resp = conn.poll_for_decision_task("test-domain", "queue")
+    assert resp["workflowExecution"]["runId"] == conn.run_id
+    assert "previousStartedEventId" not in resp
+
+    # Require a failing decision, in this case a non-existant activity type
+    attrs = {
+        "activityId": "spam",
+        "activityType": {"name": "test-activity", "version": "v1.42"},
+        "taskList": "eggs",
+    }
+    decision = {
+        "decisionType": "ScheduleActivityTask",
+        "scheduleActivityTaskDecisionAttributes": attrs,
+    }
+    conn.respond_decision_task_completed(resp["taskToken"], decisions=[decision])
+    resp = conn.poll_for_decision_task("test-domain", "queue")
+    assert resp["workflowExecution"]["runId"] == conn.run_id
+    assert resp["previousStartedEventId"] == 3
+
+
 @mock_swf_deprecated
 def test_poll_for_decision_task_when_none():
     conn = setup_workflow()