diff --git a/tests/interface_dag_elements/test_tt_function.py b/tests/interface_dag_elements/test_tt_function.py
new file mode 100644
index 000000000..e8cdca381
--- /dev/null
+++ b/tests/interface_dag_elements/test_tt_function.py
@@ -0,0 +1,117 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from ttsim.entry_point import main
+from ttsim.main_args import InputData, TTTargets
+from ttsim.main_target import MainTarget
+from ttsim.tt import group_creation_function, policy_function, policy_input
+
+if TYPE_CHECKING:
+    from types import ModuleType
+    from typing import Literal
+
+    from ttsim.typing import IntColumn
+
+
+@policy_input()
+def some_input_m() -> int:
+    pass
+
+
+@policy_input()
+def another_input_m() -> int:
+    pass
+
+
+@group_creation_function()
+def even_id(p_id: IntColumn, xnp: ModuleType) -> IntColumn:  # noqa: ARG001
+    return p_id % 2
+
+
+@policy_function()
+def pf_taking_input_and_aggregated_pf_m(
+    some_input_m: int, another_input_m_even: int
+) -> float:
+    return another_input_m_even / 2 + some_input_m
+
+
+@policy_function()
+def pf_taking_input_and_time_converted_pf_y(
+    some_input_y: float, another_input_y: float
+) -> float:
+    return another_input_y / 2 + some_input_y
+
+
+def test_aggregated_functions_are_overwritten_by_scalar_inputs(
+    xnp: ModuleType, backend: Literal["numpy", "jax"]
+):
+    column_objects_and_param_functions = {
+        ("some_input",): some_input_m,
+        ("another_input",): another_input_m,
+        ("even_id",): even_id,
+        ("pf_taking_input_and_aggregated_pf_m",): pf_taking_input_and_aggregated_pf_m,
+    }
+
+    tt_function = main(
+        main_target=MainTarget.tt_function,
+        orig_policy_objects={
+            "column_objects_and_param_functions": column_objects_and_param_functions,
+            "param_specs": {},
+        },
+        input_data=InputData.tree(
+            {
+                "p_id": xnp.array([0]),
+                "some_input_m": xnp.array([1]),
+                "another_input_m_even": 2,
+            }
+        ),
+        tt_targets=TTTargets.tree({"pf_taking_input_and_aggregated_pf_m": None}),
+        policy_date_str="2024-01-01",
+        backend=backend,
+    )
+
+    # Returns KeyError because 'another_input_m_even' was not partialled in tt_function
+    tt_function(
+        {
+            "some_input_m": xnp.array([1, 2, 3]),
+        }
+    )
+
+
+def test_time_converted_functions_are_overwritten_by_scalar_inputs(
+    xnp: ModuleType, backend: Literal["numpy", "jax"]
+):
+    column_objects_and_param_functions = {
+        ("some_input_m",): some_input_m,
+        ("another_input_m",): another_input_m,
+        ("even_id",): even_id,
+        (
+            "pf_taking_input_and_time_converted_pf_y",
+        ): pf_taking_input_and_time_converted_pf_y,
+    }
+
+    tt_function = main(
+        main_target=MainTarget.tt_function,
+        orig_policy_objects={
+            "column_objects_and_param_functions": column_objects_and_param_functions,
+            "param_specs": {},
+        },
+        input_data=InputData.tree(
+            {
+                "p_id": xnp.array([0]),
+                "some_input_m": xnp.array([1]),
+                "another_input_y": 2,
+            }
+        ),
+        tt_targets=TTTargets.tree({"pf_taking_input_and_time_converted_pf_y": None}),
+        policy_date_str="2024-01-01",
+        backend=backend,
+    )
+
+    # Returns KeyError because 'another_input_y' was not partialled in tt_function
+    tt_function(
+        {
+            "some_input_m": xnp.array([1, 2, 3]),
+        }
+    )