diff --git a/api/tests/unit_tests/core/workflow/nodes/test_list_operator.py b/api/tests/unit_tests/core/workflow/nodes/test_list_operator.py
index 53e3c93fcc99e1..0f5c8bf51ba158 100644
--- a/api/tests/unit_tests/core/workflow/nodes/test_list_operator.py
+++ b/api/tests/unit_tests/core/workflow/nodes/test_list_operator.py
@@ -2,11 +2,11 @@
 
 import pytest
 
-from core.file import File
-from core.file.models import FileTransferMethod, FileType
+from core.file import File, FileTransferMethod, FileType
 from core.variables import ArrayFileSegment
 from core.workflow.nodes.list_operator.entities import FilterBy, FilterCondition, Limit, ListOperatorNodeData, OrderBy
-from core.workflow.nodes.list_operator.node import ListOperatorNode
+from core.workflow.nodes.list_operator.exc import InvalidKeyError
+from core.workflow.nodes.list_operator.node import ListOperatorNode, _get_file_extract_string_func
 from models.workflow import WorkflowNodeExecutionStatus
 
 
@@ -109,3 +109,46 @@ def test_filter_files_by_type(list_operator_node):
         assert expected_file["tenant_id"] == result_file.tenant_id
         assert expected_file["transfer_method"] == result_file.transfer_method
         assert expected_file["related_id"] == result_file.related_id
+
+
+def test_get_file_extract_string_func():
+    # Create a File object
+    file = File(
+        tenant_id="test_tenant",
+        type=FileType.DOCUMENT,
+        transfer_method=FileTransferMethod.LOCAL_FILE,
+        filename="test_file.txt",
+        extension=".txt",
+        mime_type="text/plain",
+        remote_url="https://example.com/test_file.txt",
+        related_id="test_related_id",
+    )
+
+    # Test each case
+    assert _get_file_extract_string_func(key="name")(file) == "test_file.txt"
+    assert _get_file_extract_string_func(key="type")(file) == "document"
+    assert _get_file_extract_string_func(key="extension")(file) == ".txt"
+    assert _get_file_extract_string_func(key="mime_type")(file) == "text/plain"
+    assert _get_file_extract_string_func(key="transfer_method")(file) == "local_file"
+    assert _get_file_extract_string_func(key="url")(file) == "https://example.com/test_file.txt"
+
+    # Test with empty values
+    empty_file = File(
+        tenant_id="test_tenant",
+        type=FileType.DOCUMENT,
+        transfer_method=FileTransferMethod.LOCAL_FILE,
+        filename=None,
+        extension=None,
+        mime_type=None,
+        remote_url=None,
+        related_id="test_related_id",
+    )
+
+    assert _get_file_extract_string_func(key="name")(empty_file) == ""
+    assert _get_file_extract_string_func(key="extension")(empty_file) == ""
+    assert _get_file_extract_string_func(key="mime_type")(empty_file) == ""
+    assert _get_file_extract_string_func(key="url")(empty_file) == ""
+
+    # Test invalid key
+    with pytest.raises(InvalidKeyError):
+        _get_file_extract_string_func(key="invalid_key")