diff --git a/api/core/rag/retrieval/dataset_retrieval.py b/api/core/rag/retrieval/dataset_retrieval.py
index baf879df95..8f6c620925 100644
--- a/api/core/rag/retrieval/dataset_retrieval.py
+++ b/api/core/rag/retrieval/dataset_retrieval.py
@@ -7,7 +7,7 @@ from collections.abc import Generator, Mapping
 from typing import Any, Union, cast
 
 from flask import Flask, current_app
-from sqlalchemy import and_, or_, select
+from sqlalchemy import and_, literal, or_, select
 from sqlalchemy.orm import Session
 
 from core.app.app_config.entities import (
@@ -1036,7 +1036,7 @@ class DatasetRetrieval:
             if automatic_metadata_filters:
                 conditions = []
                 for sequence, filter in enumerate(automatic_metadata_filters):
-                    self._process_metadata_filter_func(
+                    self.process_metadata_filter_func(
                         sequence,
                         filter.get("condition"),  # type: ignore
                         filter.get("metadata_name"),  # type: ignore
@@ -1072,7 +1072,7 @@ class DatasetRetrieval:
                             value=expected_value,
                         )
                     )
-                    filters = self._process_metadata_filter_func(
+                    filters = self.process_metadata_filter_func(
                         sequence,
                         condition.comparison_operator,
                         metadata_name,
@@ -1168,8 +1168,9 @@ class DatasetRetrieval:
             return None
         return automatic_metadata_filters
 
-    def _process_metadata_filter_func(
-        self, sequence: int, condition: str, metadata_name: str, value: Any | None, filters: list
+    @classmethod
+    def process_metadata_filter_func(
+        cls, sequence: int, condition: str, metadata_name: str, value: Any | None, filters: list
     ):
         if value is None and condition not in ("empty", "not empty"):
             return filters
@@ -1218,6 +1219,18 @@ class DatasetRetrieval:
 
             case "≥" | ">=":
                 filters.append(DatasetDocument.doc_metadata[metadata_name].as_float() >= value)
+            case "in":
+                if isinstance(value, str):
+                    value_list = [v.strip() for v in value.split(",") if v.strip()]
+                elif isinstance(value, (list, tuple)):
+                    value_list = [str(v) for v in value if v is not None]
+                else:
+                    value_list = [str(value)] if value is not None else []
+
+                if not value_list:
+                    filters.append(literal(False))
+                else:
+                    filters.append(json_field.in_(value_list))
             case _:
                 pass
 
diff --git a/api/core/workflow/nodes/knowledge_retrieval/knowledge_retrieval_node.py b/api/core/workflow/nodes/knowledge_retrieval/knowledge_retrieval_node.py
index adc474bd60..8670a71aa3 100644
--- a/api/core/workflow/nodes/knowledge_retrieval/knowledge_retrieval_node.py
+++ b/api/core/workflow/nodes/knowledge_retrieval/knowledge_retrieval_node.py
@@ -6,7 +6,7 @@ from collections import defaultdict
 from collections.abc import Mapping, Sequence
 from typing import TYPE_CHECKING, Any, cast
 
-from sqlalchemy import and_, func, literal, or_, select
+from sqlalchemy import and_, func, or_, select
 from sqlalchemy.orm import sessionmaker
 
 from core.app.app_config.entities import DatasetRetrieveConfigEntity
@@ -460,7 +460,7 @@ class KnowledgeRetrievalNode(LLMUsageTrackingMixin, Node[KnowledgeRetrievalNodeD
             if automatic_metadata_filters:
                 conditions = []
                 for sequence, filter in enumerate(automatic_metadata_filters):
-                    self._process_metadata_filter_func(
+                    DatasetRetrieval.process_metadata_filter_func(
                         sequence,
                         filter.get("condition", ""),
                         filter.get("metadata_name", ""),
@@ -504,7 +504,7 @@ class KnowledgeRetrievalNode(LLMUsageTrackingMixin, Node[KnowledgeRetrievalNodeD
                             value=expected_value,
                         )
                     )
-                    filters = self._process_metadata_filter_func(
+                    filters = DatasetRetrieval.process_metadata_filter_func(
                         sequence,
                         condition.comparison_operator,
                         metadata_name,
@@ -603,87 +603,6 @@ class KnowledgeRetrievalNode(LLMUsageTrackingMixin, Node[KnowledgeRetrievalNodeD
             return [], usage
         return automatic_metadata_filters, usage
 
-    def _process_metadata_filter_func(
-        self, sequence: int, condition: str, metadata_name: str, value: Any, filters: list[Any]
-    ) -> list[Any]:
-        if value is None and condition not in ("empty", "not empty"):
-            return filters
-
-        json_field = Document.doc_metadata[metadata_name].as_string()
-
-        match condition:
-            case "contains":
-                filters.append(json_field.like(f"%{value}%"))
-
-            case "not contains":
-                filters.append(json_field.notlike(f"%{value}%"))
-
-            case "start with":
-                filters.append(json_field.like(f"{value}%"))
-
-            case "end with":
-                filters.append(json_field.like(f"%{value}"))
-            case "in":
-                if isinstance(value, str):
-                    value_list = [v.strip() for v in value.split(",") if v.strip()]
-                elif isinstance(value, (list, tuple)):
-                    value_list = [str(v) for v in value if v is not None]
-                else:
-                    value_list = [str(value)] if value is not None else []
-
-                if not value_list:
-                    filters.append(literal(False))
-                else:
-                    filters.append(json_field.in_(value_list))
-
-            case "not in":
-                if isinstance(value, str):
-                    value_list = [v.strip() for v in value.split(",") if v.strip()]
-                elif isinstance(value, (list, tuple)):
-                    value_list = [str(v) for v in value if v is not None]
-                else:
-                    value_list = [str(value)] if value is not None else []
-
-                if not value_list:
-                    filters.append(literal(True))
-                else:
-                    filters.append(json_field.notin_(value_list))
-
-            case "is" | "=":
-                if isinstance(value, str):
-                    filters.append(json_field == value)
-                elif isinstance(value, (int, float)):
-                    filters.append(Document.doc_metadata[metadata_name].as_float() == value)
-
-            case "is not" | "≠":
-                if isinstance(value, str):
-                    filters.append(json_field != value)
-                elif isinstance(value, (int, float)):
-                    filters.append(Document.doc_metadata[metadata_name].as_float() != value)
-
-            case "empty":
-                filters.append(Document.doc_metadata[metadata_name].is_(None))
-
-            case "not empty":
-                filters.append(Document.doc_metadata[metadata_name].isnot(None))
-
-            case "before" | "<":
-                filters.append(Document.doc_metadata[metadata_name].as_float() < value)
-
-            case "after" | ">":
-                filters.append(Document.doc_metadata[metadata_name].as_float() > value)
-
-            case "≤" | "<=":
-                filters.append(Document.doc_metadata[metadata_name].as_float() <= value)
-
-            case "≥" | ">=":
-                filters.append(Document.doc_metadata[metadata_name].as_float() >= value)
-
-            case _:
-                pass
-
-        return filters
-
     @classmethod
     def _extract_variable_selector_to_variable_mapping(
         cls,
diff --git a/api/tests/unit_tests/core/rag/retrieval/test_dataset_retrieval_metadata_filter.py b/api/tests/unit_tests/core/rag/retrieval/test_dataset_retrieval_metadata_filter.py
new file mode 100644
index 0000000000..07d6e51e4b
--- /dev/null
+++ b/api/tests/unit_tests/core/rag/retrieval/test_dataset_retrieval_metadata_filter.py
@@ -0,0 +1,873 @@
+"""
+Unit tests for DatasetRetrieval.process_metadata_filter_func.
+
+This module provides comprehensive test coverage for the process_metadata_filter_func
+method in the DatasetRetrieval class, which is responsible for building SQLAlchemy
+filter expressions based on metadata filtering conditions.
+
+Conditions Tested:
+==================
+1. **String Conditions**: contains, not contains, start with, end with
+2. **Equality Conditions**: is / =, is not / ≠
+3. **Null Conditions**: empty, not empty
+4. **Numeric Comparisons**: before / <, after / >, ≤ / <=, ≥ / >=
+5. **List Conditions**: in
+6. **Edge Cases**: None values, different data types (str, int, float)
+
+Test Architecture:
+==================
+- Direct instantiation of DatasetRetrieval
+- Mocking of DatasetDocument model attributes
+- Verification of SQLAlchemy filter expressions
+- Follows Arrange-Act-Assert (AAA) pattern
+
+Running Tests:
+==============
+    # Run all tests in this module
+    uv run --project api pytest \
+        api/tests/unit_tests/core/rag/retrieval/test_dataset_retrieval_metadata_filter.py -v
+
+    # Run a specific test
+    uv run --project api pytest \
+        api/tests/unit_tests/core/rag/retrieval/test_dataset_retrieval_metadata_filter.py::\
+TestProcessMetadataFilterFunc::test_contains_condition -v
+"""
+
+from unittest.mock import MagicMock
+
+import pytest
+
+from core.rag.retrieval.dataset_retrieval import DatasetRetrieval
+
+
+class TestProcessMetadataFilterFunc:
+    """
+    Comprehensive test suite for process_metadata_filter_func method.
+
+    This test class validates all metadata filtering conditions supported by
+    the DatasetRetrieval class, including string operations, numeric comparisons,
+    null checks, and list operations.
+
+    Method Signature:
+    ==================
+    def process_metadata_filter_func(
+        self, sequence: int, condition: str, metadata_name: str, value: Any | None, filters: list
+    ) -> list:
+
+    The method builds SQLAlchemy filter expressions by:
+    1. Validating value is not None (except for empty/not empty conditions)
+    2. Using DatasetDocument.doc_metadata JSON field operations
+    3. Adding appropriate SQLAlchemy expressions to the filters list
+    4. Returning the updated filters list
+
+    Mocking Strategy:
+    ==================
+    - Mock DatasetDocument.doc_metadata to avoid database dependencies
+    - Verify filter expressions are created correctly
+    - Test with various data types (str, int, float, list)
+    """
+
+    @pytest.fixture
+    def retrieval(self):
+        """
+        Create a DatasetRetrieval instance for testing.
+
+        Returns:
+            DatasetRetrieval: Instance to test process_metadata_filter_func
+        """
+        return DatasetRetrieval()
+
+    @pytest.fixture
+    def mock_doc_metadata(self):
+        """
+        Mock the DatasetDocument.doc_metadata JSON field.
+
+        The method uses DatasetDocument.doc_metadata[metadata_name] to access
+        JSON fields. We mock this to avoid database dependencies.
+
+        Returns:
+            Mock: Mocked doc_metadata attribute
+        """
+        mock_metadata_field = MagicMock()
+
+        # Create mock for string access
+        mock_string_access = MagicMock()
+        mock_string_access.like = MagicMock()
+        mock_string_access.notlike = MagicMock()
+        mock_string_access.__eq__ = MagicMock(return_value=MagicMock())
+        mock_string_access.__ne__ = MagicMock(return_value=MagicMock())
+        mock_string_access.in_ = MagicMock(return_value=MagicMock())
+
+        # Create mock for float access (for numeric comparisons)
+        mock_float_access = MagicMock()
+        mock_float_access.__eq__ = MagicMock(return_value=MagicMock())
+        mock_float_access.__ne__ = MagicMock(return_value=MagicMock())
+        mock_float_access.__lt__ = MagicMock(return_value=MagicMock())
+        mock_float_access.__gt__ = MagicMock(return_value=MagicMock())
+        mock_float_access.__le__ = MagicMock(return_value=MagicMock())
+        mock_float_access.__ge__ = MagicMock(return_value=MagicMock())
+
+        # Create mock for null checks
+        mock_null_access = MagicMock()
+        mock_null_access.is_ = MagicMock(return_value=MagicMock())
+        mock_null_access.isnot = MagicMock(return_value=MagicMock())
+
+        # Setup __getitem__ to return appropriate mock based on usage
+        def getitem_side_effect(name):
+            if name in ["author", "title", "category"]:
+                return mock_string_access
+            elif name in ["year", "price", "rating"]:
+                return mock_float_access
+            else:
+                return mock_string_access
+
+        mock_metadata_field.__getitem__ = MagicMock(side_effect=getitem_side_effect)
+        mock_metadata_field.as_string.return_value = mock_string_access
+        mock_metadata_field.as_float.return_value = mock_float_access
+        mock_metadata_field[metadata_name:str].is_ = mock_null_access.is_
+        mock_metadata_field[metadata_name:str].isnot = mock_null_access.isnot
+
+        return mock_metadata_field
+
+    # ==================== String Condition Tests ====================
+
+    def test_contains_condition_string_value(self, retrieval):
+        """
+        Test 'contains' condition with string value.
+
+        Verifies:
+        - Filters list is populated with LIKE expression
+        - Pattern matching uses %value% syntax
+        """
+        filters = []
+        sequence = 0
+        condition = "contains"
+        metadata_name = "author"
+        value = "John"
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_not_contains_condition(self, retrieval):
+        """
+        Test 'not contains' condition.
+
+        Verifies:
+        - Filters list is populated with NOT LIKE expression
+        - Pattern matching uses %value% syntax with negation
+        """
+        filters = []
+        sequence = 0
+        condition = "not contains"
+        metadata_name = "title"
+        value = "banned"
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_start_with_condition(self, retrieval):
+        """
+        Test 'start with' condition.
+
+        Verifies:
+        - Filters list is populated with LIKE expression
+        - Pattern matching uses value% syntax
+        """
+        filters = []
+        sequence = 0
+        condition = "start with"
+        metadata_name = "category"
+        value = "tech"
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_end_with_condition(self, retrieval):
+        """
+        Test 'end with' condition.
+
+        Verifies:
+        - Filters list is populated with LIKE expression
+        - Pattern matching uses %value syntax
+        """
+        filters = []
+        sequence = 0
+        condition = "end with"
+        metadata_name = "filename"
+        value = ".pdf"
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    # ==================== Equality Condition Tests ====================
+
+    def test_is_condition_with_string_value(self, retrieval):
+        """
+        Test 'is' (=) condition with string value.
+
+        Verifies:
+        - Filters list is populated with equality expression
+        - String comparison is used
+        """
+        filters = []
+        sequence = 0
+        condition = "is"
+        metadata_name = "author"
+        value = "Jane Doe"
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_equals_condition_with_string_value(self, retrieval):
+        """
+        Test '=' condition with string value.
+
+        Verifies:
+        - Same behavior as 'is' condition
+        - String comparison is used
+        """
+        filters = []
+        sequence = 0
+        condition = "="
+        metadata_name = "category"
+        value = "technology"
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_is_condition_with_int_value(self, retrieval):
+        """
+        Test 'is' condition with integer value.
+
+        Verifies:
+        - Numeric comparison is used
+        - as_float() is called on the metadata field
+        """
+        filters = []
+        sequence = 0
+        condition = "is"
+        metadata_name = "year"
+        value = 2023
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_is_condition_with_float_value(self, retrieval):
+        """
+        Test 'is' condition with float value.
+
+        Verifies:
+        - Numeric comparison is used
+        - as_float() is called on the metadata field
+        """
+        filters = []
+        sequence = 0
+        condition = "is"
+        metadata_name = "price"
+        value = 19.99
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_is_not_condition_with_string_value(self, retrieval):
+        """
+        Test 'is not' (≠) condition with string value.
+
+        Verifies:
+        - Filters list is populated with inequality expression
+        - String comparison is used
+        """
+        filters = []
+        sequence = 0
+        condition = "is not"
+        metadata_name = "author"
+        value = "Unknown"
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_not_equals_condition(self, retrieval):
+        """
+        Test '≠' condition with string value.
+
+        Verifies:
+        - Same behavior as 'is not' condition
+        - Inequality expression is used
+        """
+        filters = []
+        sequence = 0
+        condition = "≠"
+        metadata_name = "category"
+        value = "archived"
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_is_not_condition_with_numeric_value(self, retrieval):
+        """
+        Test 'is not' condition with numeric value.
+
+        Verifies:
+        - Numeric inequality comparison is used
+        - as_float() is called on the metadata field
+        """
+        filters = []
+        sequence = 0
+        condition = "is not"
+        metadata_name = "year"
+        value = 2000
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    # ==================== Null Condition Tests ====================
+
+    def test_empty_condition(self, retrieval):
+        """
+        Test 'empty' condition (null check).
+
+        Verifies:
+        - Filters list is populated with IS NULL expression
+        - Value can be None for this condition
+        """
+        filters = []
+        sequence = 0
+        condition = "empty"
+        metadata_name = "author"
+        value = None
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_not_empty_condition(self, retrieval):
+        """
+        Test 'not empty' condition (not null check).
+
+        Verifies:
+        - Filters list is populated with IS NOT NULL expression
+        - Value can be None for this condition
+        """
+        filters = []
+        sequence = 0
+        condition = "not empty"
+        metadata_name = "description"
+        value = None
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    # ==================== Numeric Comparison Tests ====================
+
+    def test_before_condition(self, retrieval):
+        """
+        Test 'before' (<) condition.
+
+        Verifies:
+        - Filters list is populated with less than expression
+        - Numeric comparison is used
+        """
+        filters = []
+        sequence = 0
+        condition = "before"
+        metadata_name = "year"
+        value = 2020
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_less_than_condition(self, retrieval):
+        """
+        Test '<' condition.
+
+        Verifies:
+        - Same behavior as 'before' condition
+        - Less than expression is used
+        """
+        filters = []
+        sequence = 0
+        condition = "<"
+        metadata_name = "price"
+        value = 100.0
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_after_condition(self, retrieval):
+        """
+        Test 'after' (>) condition.
+
+        Verifies:
+        - Filters list is populated with greater than expression
+        - Numeric comparison is used
+        """
+        filters = []
+        sequence = 0
+        condition = "after"
+        metadata_name = "year"
+        value = 2020
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_greater_than_condition(self, retrieval):
+        """
+        Test '>' condition.
+
+        Verifies:
+        - Same behavior as 'after' condition
+        - Greater than expression is used
+        """
+        filters = []
+        sequence = 0
+        condition = ">"
+        metadata_name = "rating"
+        value = 4.5
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_less_than_or_equal_condition_unicode(self, retrieval):
+        """
+        Test '≤' condition.
+
+        Verifies:
+        - Filters list is populated with less than or equal expression
+        - Numeric comparison is used
+        """
+        filters = []
+        sequence = 0
+        condition = "≤"
+        metadata_name = "price"
+        value = 50.0
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_less_than_or_equal_condition_ascii(self, retrieval):
+        """
+        Test '<=' condition.
+
+        Verifies:
+        - Same behavior as '≤' condition
+        - Less than or equal expression is used
+        """
+        filters = []
+        sequence = 0
+        condition = "<="
+        metadata_name = "year"
+        value = 2023
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_greater_than_or_equal_condition_unicode(self, retrieval):
+        """
+        Test '≥' condition.
+
+        Verifies:
+        - Filters list is populated with greater than or equal expression
+        - Numeric comparison is used
+        """
+        filters = []
+        sequence = 0
+        condition = "≥"
+        metadata_name = "rating"
+        value = 3.5
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_greater_than_or_equal_condition_ascii(self, retrieval):
+        """
+        Test '>=' condition.
+
+        Verifies:
+        - Same behavior as '≥' condition
+        - Greater than or equal expression is used
+        """
+        filters = []
+        sequence = 0
+        condition = ">="
+        metadata_name = "year"
+        value = 2000
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    # ==================== List/In Condition Tests ====================
+
+    def test_in_condition_with_comma_separated_string(self, retrieval):
+        """
+        Test 'in' condition with comma-separated string value.
+
+        Verifies:
+        - String is split into list
+        - Whitespace is trimmed from each value
+        - IN expression is created
+        """
+        filters = []
+        sequence = 0
+        condition = "in"
+        metadata_name = "category"
+        value = "tech, science,  AI  "
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_in_condition_with_list_value(self, retrieval):
+        """
+        Test 'in' condition with list value.
+
+        Verifies:
+        - List is processed correctly
+        - None values are filtered out
+        - IN expression is created with valid values
+        """
+        filters = []
+        sequence = 0
+        condition = "in"
+        metadata_name = "tags"
+        value = ["python", "javascript", None, "golang"]
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_in_condition_with_tuple_value(self, retrieval):
+        """
+        Test 'in' condition with tuple value.
+
+        Verifies:
+        - Tuple is processed like a list
+        - IN expression is created
+        """
+        filters = []
+        sequence = 0
+        condition = "in"
+        metadata_name = "category"
+        value = ("tech", "science", "ai")
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_in_condition_with_empty_string(self, retrieval):
+        """
+        Test 'in' condition with empty string value.
+
+        Verifies:
+        - Empty string results in literal(False) filter
+        - No valid values to match
+        """
+        filters = []
+        sequence = 0
+        condition = "in"
+        metadata_name = "category"
+        value = ""
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+        # Verify it's a literal(False) expression
+        # This is a bit tricky to test without access to the actual expression
+
+    def test_in_condition_with_only_whitespace(self, retrieval):
+        """
+        Test 'in' condition with whitespace-only string value.
+
+        Verifies:
+        - Whitespace-only string results in literal(False) filter
+        - All values are stripped and filtered out
+        """
+        filters = []
+        sequence = 0
+        condition = "in"
+        metadata_name = "category"
+        value = "   ,   ,   "
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_in_condition_with_single_string(self, retrieval):
+        """
+        Test 'in' condition with single non-comma string.
+
+        Verifies:
+        - Single string is treated as single-item list
+        - IN expression is created with one value
+        """
+        filters = []
+        sequence = 0
+        condition = "in"
+        metadata_name = "category"
+        value = "technology"
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    # ==================== Edge Case Tests ====================
+
+    def test_none_value_with_non_empty_condition(self, retrieval):
+        """
+        Test None value with conditions that require value.
+
+        Verifies:
+        - Original filters list is returned unchanged
+        - No filter is added for None values (except empty/not empty)
+        """
+        filters = []
+        sequence = 0
+        condition = "contains"
+        metadata_name = "author"
+        value = None
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 0  # No filter added
+
+    def test_none_value_with_equals_condition(self, retrieval):
+        """
+        Test None value with 'is' (=) condition.
+
+        Verifies:
+        - Original filters list is returned unchanged
+        - No filter is added for None values
+        """
+        filters = []
+        sequence = 0
+        condition = "is"
+        metadata_name = "author"
+        value = None
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 0
+
+    def test_none_value_with_numeric_condition(self, retrieval):
+        """
+        Test None value with numeric comparison condition.
+
+        Verifies:
+        - Original filters list is returned unchanged
+        - No filter is added for None values
+        """
+        filters = []
+        sequence = 0
+        condition = ">"
+        metadata_name = "year"
+        value = None
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 0
+
+    def test_existing_filters_preserved(self, retrieval):
+        """
+        Test that existing filters are preserved.
+
+        Verifies:
+        - Existing filters in the list are not removed
+        - New filters are appended to the list
+        """
+        existing_filter = MagicMock()
+        filters = [existing_filter]
+        sequence = 0
+        condition = "contains"
+        metadata_name = "author"
+        value = "test"
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 2
+        assert filters[0] == existing_filter
+
+    def test_multiple_filters_accumulated(self, retrieval):
+        """
+        Test multiple calls to accumulate filters.
+
+        Verifies:
+        - Each call adds a new filter to the list
+        - All filters are preserved across calls
+        """
+        filters = []
+
+        # First filter
+        retrieval.process_metadata_filter_func(0, "contains", "author", "John", filters)
+        assert len(filters) == 1
+
+        # Second filter
+        retrieval.process_metadata_filter_func(1, ">", "year", 2020, filters)
+        assert len(filters) == 2
+
+        # Third filter
+        retrieval.process_metadata_filter_func(2, "is", "category", "tech", filters)
+        assert len(filters) == 3
+
+    def test_unknown_condition(self, retrieval):
+        """
+        Test unknown/unsupported condition.
+
+        Verifies:
+        - Original filters list is returned unchanged
+        - No filter is added for unknown conditions
+        """
+        filters = []
+        sequence = 0
+        condition = "unknown_condition"
+        metadata_name = "author"
+        value = "test"
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 0
+
+    def test_empty_string_value_with_contains(self, retrieval):
+        """
+        Test empty string value with 'contains' condition.
+
+        Verifies:
+        - Filter is added even with empty string
+        - LIKE expression is created
+        """
+        filters = []
+        sequence = 0
+        condition = "contains"
+        metadata_name = "author"
+        value = ""
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_special_characters_in_value(self, retrieval):
+        """
+        Test special characters in value string.
+
+        Verifies:
+        - Special characters are handled in value
+        - LIKE expression is created correctly
+        """
+        filters = []
+        sequence = 0
+        condition = "contains"
+        metadata_name = "title"
+        value = "C++ & Python's features"
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_zero_value_with_numeric_condition(self, retrieval):
+        """
+        Test zero value with numeric comparison condition.
+
+        Verifies:
+        - Zero is treated as valid value
+        - Numeric comparison is performed
+        """
+        filters = []
+        sequence = 0
+        condition = ">"
+        metadata_name = "price"
+        value = 0
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_negative_value_with_numeric_condition(self, retrieval):
+        """
+        Test negative value with numeric comparison condition.
+
+        Verifies:
+        - Negative numbers are handled correctly
+        - Numeric comparison is performed
+        """
+        filters = []
+        sequence = 0
+        condition = "<"
+        metadata_name = "temperature"
+        value = -10.5
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1
+
+    def test_float_value_with_integer_comparison(self, retrieval):
+        """
+        Test float value with numeric comparison condition.
+
+        Verifies:
+        - Float values work correctly
+        - Numeric comparison is performed
+        """
+        filters = []
+        sequence = 0
+        condition = ">="
+        metadata_name = "rating"
+        value = 4.5
+
+        result = retrieval.process_metadata_filter_func(sequence, condition, metadata_name, value, filters)
+
+        assert result == filters
+        assert len(filters) == 1