code: def test_create_should_raise_error_on_both_prefix_and_runs():
      real_client = pymongo.MongoClient()
      with pytest.raises(
          ValueError,
          match="Cannot pass both collection and a collection prefix.",
      ):
          MongoObserver(
              client=real_client,
              collection_prefix="myprefix",
              collection="some_collection",
          )
  
imports: import datetime
  import os
  import sys
  from glob import glob
  import mock
  import pytest
  from sacred.metrics_logger import ScalarMetricLogEntry, linearize_metrics
  import gridfs
  from mongomock.gridfs import enable_gridfs_integration
  from .failing_mongo_mock import FailingMongoClient
  from sacred.dependencies import get_digest
  from sacred.observers.mongo import MongoObserver, force_bson_encodeable
label_desc: Use image node_id 3 for calling a global function with example usage: test_create_should_raise_error_on_both_prefix_and_runs() without return types