Test interpolation function checking (and remove checking of type annotations)

Dynamically checking of type annotations like this is flaky due to how Python internally handles type annotations

Author: VeckoTheGecko

parcels/field.py

@@ -124,19 +124,11 @@ def _validate_interp_function(self, func: Callable) -> None:
                 raise ValueError(
                     f"Parameter '{_name2}' has incorrect parameter kind. Expected {param1.kind}, got {param2.kind}"
                 )
-            if param1.annotation != param2.annotation:
+            if param1.name != param2.name:
                 raise ValueError(
-                    f"Parameter '{_name2}' has incorrect type annotation. Expected {param1.annotation}, got {param2.annotation}"
+                    f"Parameter '{_name2}' has incorrect name. Expected '{param1.name}', got '{param2.name}'"
                 )
 
-        return_annotation = func_sig.return_annotation
-        template_return = template_sig.return_annotation
-
-        if return_annotation != template_return:
-            raise ValueError(
-                f"Interpolation function has incorrect return type. Expected {template_return}, got {return_annotation}"
-            )
-
     def __init__(
         self,
         name: str,
@@ -345,20 +337,6 @@ def __contains__(self, key: str):
 class VectorField:
     """VectorField class that holds vector field data needed to execute particles."""
 
-    @staticmethod
-    def _vector_interp_template(
-        self,
-        ti: int,
-        position: dict[str, tuple[int, float | np.ndarray]],
-        tau: np.float32 | np.float64,
-        t: np.float32 | np.float64,
-        z: np.float32 | np.float64,
-        y: np.float32 | np.float64,
-        x: np.float32 | np.float64,
-    ) -> np.float32 | np.float64:
-        """Template function used for the signature check of the lateral interpolation methods."""
-        return 0.0
-
     def _validate_vector_interp_function(self, func: Callable):
         """Ensures that the function has the correct signature."""
         expected_params = ["ti", "ei", "bcoords", "t", "z", "y", "x"]

tests/v4/test_field.py

@@ -1,9 +1,11 @@
+from __future__ import annotations
+
 import numpy as np
 import pytest
 import uxarray as ux
 import xarray as xr
 
-from parcels import Field, UXPiecewiseConstantFace, UXPiecewiseLinearNode, xgcm
+from parcels import Field, UXPiecewiseConstantFace, UXPiecewiseLinearNode, VectorField, xgcm
 from parcels._datasets.structured.generic import T as T_structured
 from parcels._datasets.structured.generic import datasets as datasets_structured
 from parcels._datasets.unstructured.generic import datasets as datasets_unstructured
@@ -115,6 +117,38 @@ def test_vectorfield_init_different_time_intervals():
     ...
 
 
+def test_field_invalid_interpolator():
+    """Test that Field initialization fails with invalid interpolation methods."""
+    ds = datasets_structured["ds_2d_left"]
+    grid = XGrid(xgcm.Grid(ds))
+
+    def invalid_interpolator_wrong_signature(self, ti, position, tau, t, z, y, invalid):
+        return 0.0
+
+    # Test invalid interpolator with wrong signature
+    with pytest.raises(ValueError, match=".*incorrect name.*"):
+        Field(name="test", data=ds["data_g"], grid=grid, interp_method=invalid_interpolator_wrong_signature)
+
+
+@pytest.mark.xfail
+def test_vectorfield_invalid_interpolator():
+    """Test that VectorField initialization fails with invalid interpolation methods."""
+    ds = datasets_structured["ds_2d_left"]
+    grid = XGrid(xgcm.Grid(ds))
+
+    def invalid_interpolator_wrong_signature(self):
+        # Missing required parameters from _interp_template signature
+        return 0.0
+
+    # Create component fields
+    U = Field(name="U", data=ds["data_g"], grid=grid)
+    V = Field(name="V", data=ds["data_g"], grid=grid)
+
+    # Test invalid interpolator with wrong signature
+    with pytest.raises(ValueError, match=".*incorrect name.*"):
+        VectorField(name="UV", U=U, V=V, vector_interp_method=invalid_interpolator_wrong_signature)
+
+
 def test_field_unstructured_z_linear():
     """Tests correctness of piecewise constant and piecewise linear interpolation methods on an unstructured grid with a vertical coordinate.
     The example dataset is a FESOM2 square Delaunay grid with uniform z-coordinate. Cell centered and layer registered data are defined to be