Adding "no start_workflow()" test

Fairly simple test, should help to provide some extra peace of mind.

openassessment/workflow/test/test_api.py

@@ -278,6 +278,30 @@ class TestAssessmentWorkflowApi(CacheResetTest):
         workflow = workflow_api.create_workflow(submission["uuid"], data["steps"], ON_INIT_PARAMS)
         workflow_api.get_workflow_for_submission(workflow["uuid"], {})
 
+    def test_preexisting_workflow(self):
+        """
+        Verifies that even if a workflow does not go through start_workflow, it won't blow up.
+        update_from_assessments() will go through _get_steps(), and add a staff step to the workflow
+        even if it was created without one initially.
+        """
+        submission = sub_api.create_submission({
+            "student_id": "test student",
+            "course_id": "test course",
+            "item_id": "test item",
+            "item_type": "openassessment",
+        }, "test answer")
+
+        # Create the model object directly, bypassing start_workflow()
+        workflow = AssessmentWorkflow.objects.create(
+            submission_uuid=submission["uuid"],
+            status=AssessmentWorkflow.STATUS.waiting,
+            course_id="test course",
+            item_id="test item"
+        )
+
+        # This call will throw exceptions if the workflow is in an invalid state
+        workflow_api.update_from_assessments(submission["uuid"], {})
+
     def test_get_status_counts(self):
         # Initially, the counts should all be zero
         counts = workflow_api.get_status_counts(