diff --git a/.github/workflows/_test.yml b/.github/workflows/_test.yml
index a2361b45..e4c3687a 100644
--- a/.github/workflows/_test.yml
+++ b/.github/workflows/_test.yml
@@ -43,7 +43,7 @@ jobs:
         - name: Install Python toolchains
           run: |
             source .venv/bin/activate
-            pip install maturin pytest mypy
+            pip install maturin mypy pytest pytest-asyncio
         - name: Python build
           run: |
             source .venv/bin/activate
diff --git a/pyproject.toml b/pyproject.toml
index 4514bf9f..9fe45190 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -29,7 +29,7 @@ module-name = "cocoindex._engine"
 features = ["pyo3/extension-module"]
 
 [project.optional-dependencies]
-dev = ["pytest", "ruff", "mypy", "pre-commit"]
+dev = ["pytest", "pytest-asyncio", "ruff", "mypy", "pre-commit"]
 
 embeddings = ["sentence-transformers>=3.3.1"]
 
diff --git a/python/cocoindex/tests/test_transform_flow.py b/python/cocoindex/tests/test_transform_flow.py
new file mode 100644
index 00000000..67154430
--- /dev/null
+++ b/python/cocoindex/tests/test_transform_flow.py
@@ -0,0 +1,103 @@
+import typing
+from dataclasses import dataclass
+from typing import Any
+
+import pytest
+
+import cocoindex
+
+
+@dataclass
+class Child:
+    value: int
+
+
+@dataclass
+class Parent:
+    children: list[Child]
+
+
+# Fixture to initialize CocoIndex library
+@pytest.fixture(scope="session", autouse=True)
+def init_cocoindex() -> typing.Generator[None, None, None]:
+    cocoindex.init()
+    yield
+
+
+@cocoindex.op.function()
+def add_suffix(text: str) -> str:
+    """Append ' world' to the input text."""
+    return f"{text} world"
+
+
+@cocoindex.transform_flow()
+def simple_transform(text: cocoindex.DataSlice[str]) -> cocoindex.DataSlice[str]:
+    """Transform flow that applies add_suffix to input text."""
+    return text.transform(add_suffix)
+
+
+@cocoindex.op.function()
+def extract_value(value: int) -> int:
+    """Extracts the value."""
+    return value
+
+
+@cocoindex.transform_flow()
+def for_each_transform(
+    data: cocoindex.DataSlice[Parent],
+) -> cocoindex.DataSlice[Any]:
+    """Transform flow that processes child rows to extract values."""
+    with data["children"].row() as child:
+        child["new_field"] = child["value"].transform(extract_value)
+    return data
+
+
+def test_simple_transform_flow() -> None:
+    """Test the simple transform flow."""
+    input_text = "hello"
+    result = simple_transform.eval(input_text)
+    assert result == "hello world", f"Expected 'hello world', got {result}"
+
+    result = simple_transform.eval("")
+    assert result == " world", f"Expected ' world', got {result}"
+
+
+@pytest.mark.asyncio
+async def test_simple_transform_flow_async() -> None:
+    """Test the simple transform flow asynchronously."""
+    input_text = "async"
+    result = await simple_transform.eval_async(input_text)
+    assert result == "async world", f"Expected 'async world', got {result}"
+
+
+def test_for_each_transform_flow() -> None:
+    """Test the complex transform flow with child rows."""
+    input_data = Parent(children=[Child(1), Child(2), Child(3)])
+    result = for_each_transform.eval(input_data)
+    expected = {
+        "children": [
+            {"value": 1, "new_field": 1},
+            {"value": 2, "new_field": 2},
+            {"value": 3, "new_field": 3},
+        ]
+    }
+    assert result == expected, f"Expected {expected}, got {result}"
+
+    input_data = Parent(children=[])
+    result = for_each_transform.eval(input_data)
+    assert result == {"children": []}, f"Expected {{'children': []}}, got {result}"
+
+
+@pytest.mark.asyncio
+async def test_for_each_transform_flow_async() -> None:
+    """Test the complex transform flow asynchronously."""
+    input_data = Parent(children=[Child(4), Child(5)])
+    result = await for_each_transform.eval_async(input_data)
+    expected = {
+        "children": [
+            {"value": 4, "new_field": 4},
+            {"value": 5, "new_field": 5},
+        ]
+    }
+
+    assert result == expected, f"Expected {expected}, got {result}"