class_docstr: Test InMemoryDocumentStore's specific features
class_docstr_tok: ["Test","InMemoryDocumentStore","'s","specific","features"]
code: def test_bm25_retrieval_with_empty_document_store(
      self, document_store: InMemoryDocumentStore, caplog
  ):
      caplog.set_level(logging.INFO)
      # Tests if the bm25_retrieval method correctly returns an empty list when there are no documents in the DocumentStore.
      results = document_store.bm25_retrieval(
          query="How to test this?", top_k=2
      )
      assert len(results) == 0
      assert (
          "No documents found for BM25 retrieval. Returning empty list."
          in caplog.text
      )
  
imports: import logging
  from unittest.mock import patch
  import pandas
  import pytest
  from haystack import Document
  from haystack.document_stores.errors import DocumentStoreError, DuplicateDocumentError
  from haystack.document_stores.in_memory import InMemoryDocumentStore
  from haystack.testing.document_store import DocumentStoreBaseTests
label_desc: Use image node_id 7 for calling the TestMemoryDocumentStore obj's underlying member method code with example usage: obj.test_bm25_retrieval_with_empty_document_store(document_store, caplog) without return types