def _simulate_externally_added_docs(self, index_name, docs, check_only_in_external_cache: str = None):
        """helper function to simulate another client adding docs

        Args:
            docs: list of docs to add with add_documents()
            check_only_in_external_cache: a string to check ends up in the simulated
                external cache, but not in the local cache (it should be a field in
                'docs' but not previously indexed).
        """
        if check_only_in_external_cache is not None:
            assert check_only_in_external_cache not in \
                   index_meta_cache.get_cache()[index_name].properties[TensorField.chunks]["properties"]
            assert check_only_in_external_cache not in \
                   index_meta_cache.get_cache()[index_name].properties

        # save the state of the cache:
        cache_t0 = copy.deepcopy(index_meta_cache.get_cache())
        # mock external party indexing something:
        self.add_documents(
            config=self.config, add_docs_params=AddDocsParams(index_name=index_name,
                docs=docs, auto_refresh=True, device="cpu"))

        if check_only_in_external_cache is not None:
            assert (
                    check_only_in_external_cache
                    in index_meta_cache.get_cache()[index_name].properties[TensorField.chunks]["properties"]
                   ) or (
                    check_only_in_external_cache
                    in index_meta_cache.get_cache()[index_name].properties
            )
        # set cache to t0 state:
        index_meta_cache.index_info_cache = copy.deepcopy(cache_t0)
        # search refreshes index cache every 2 seconds
        time.sleep(2.1)
        if check_only_in_external_cache is not None:
            assert check_only_in_external_cache not in \
                   index_meta_cache.get_cache()[index_name].properties[TensorField.chunks]["properties"]
            assert check_only_in_external_cache not in \
                   index_meta_cache.get_cache()[index_name].properties
helper function to simulate another client adding docs

        Args:
            docs: list of docs to add with add_documents()
            check_only_in_external_cache: a string to check ends up in the simulated
                external cache, but not in the local cache (it should be a field in
                'docs' but not previously indexed).
        
tests/integ_tests/tensor_search/test_index_meta_cache.py