From 921eaf86dccb1cc6014691063f1f89403655f4e5 Mon Sep 17 00:00:00 2001
From: Vecko <36369090+VeckoTheGecko@users.noreply.github.com>
Date: Mon, 2 Mar 2026 16:40:05 +0100
Subject: [PATCH 1/3] Move file

---
 {tests-v3 => tests}/test_typing.py | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
 rename {tests-v3 => tests}/test_typing.py (100%)

diff --git a/tests-v3/test_typing.py b/tests/test_typing.py
similarity index 100%
rename from tests-v3/test_typing.py
rename to tests/test_typing.py

From f907ef21e8611ebca0ef17c956171f221d29ce23 Mon Sep 17 00:00:00 2001
From: Vecko <36369090+VeckoTheGecko@users.noreply.github.com>
Date: Mon, 2 Mar 2026 16:58:10 +0100
Subject: [PATCH 2/3] Update _validate_against_pure_literal

Also cleaned out the test_typing.py and _typing.py modules
---
 src/parcels/_typing.py | 20 ++++++++++++--------
 tests/test_typing.py   | 31 ++++++++++---------------------
 2 files changed, 22 insertions(+), 29 deletions(-)

diff --git a/src/parcels/_typing.py b/src/parcels/_typing.py
index 7c2e12b8fd..8558cbb5df 100644
--- a/src/parcels/_typing.py
+++ b/src/parcels/_typing.py
@@ -39,24 +39,28 @@
 KernelFunction = Callable[..., None]
 
 
+def _is_xarray_object(obj):  # with no imports
+    try:
+        return "xarray.core" in obj.__module__
+    except AttributeError:
+        return False
+
+
 def _validate_against_pure_literal(value, typing_literal):
     """Uses a Literal type alias to validate.
 
     Can't be used with ``Literal[...] | None`` etc. as its not a pure literal.
     """
+    if _is_xarray_object(
+        value
+    ):  # Xarray objects don't work normally in `in` statements due to https://github.com/pydata/xarray/issues/11209
+        raise ValueError(f"Invalid input type {type(value)}")
+
     if value not in get_args(typing_literal):
         msg = f"Invalid value {value!r}. Valid options are {get_args(typing_literal)!r}"
         raise ValueError(msg)
 
 
 # Assertion functions to clean user input
-def assert_valid_interp_method(value: Any):
-    _validate_against_pure_literal(value, InterpMethodOption)
-
-
 def assert_valid_mesh(value: Any):
     _validate_against_pure_literal(value, Mesh)
-
-
-def assert_valid_gridindexingtype(value: Any):
-    _validate_against_pure_literal(value, GridIndexingType)
diff --git a/tests/test_typing.py b/tests/test_typing.py
index f4efba3efd..4f1d3e0c56 100644
--- a/tests/test_typing.py
+++ b/tests/test_typing.py
@@ -1,31 +1,20 @@
+import numpy as np
 import pytest
+import xarray as xr
 
 from parcels._typing import (
-    assert_valid_gridindexingtype,
-    assert_valid_interp_method,
     assert_valid_mesh,
 )
 
-validators = (
-    assert_valid_interp_method,
-    assert_valid_mesh,
-    assert_valid_gridindexingtype,
-)
-
-
-@pytest.mark.parametrize("validator", validators)
-def test_invalid_option(validator):
-    with pytest.raises(ValueError):
-        validator("invalid option")
 
+def test_invalid_assert_valid_mesh():
+    with pytest.raises(ValueError, match="Invalid value"):
+        assert_valid_mesh("invalid option")
 
-validation_mapping = [
-    (assert_valid_interp_method, "nearest"),
-    (assert_valid_mesh, "spherical"),
-    (assert_valid_gridindexingtype, "pop"),
-]
+    ds = xr.Dataset({"A": (("a", "b"), np.arange(20).reshape(4, 5))})
+    with pytest.raises(ValueError, match="Invalid input type"):
+        assert_valid_mesh(ds)
 
 
-@pytest.mark.parametrize("validator, value", validation_mapping)
-def test_valid_option(validator, value):
-    validator(value)
+def test_assert_valid_mesh():
+    assert_valid_mesh("spherical")

From 34b4b0960c04cffd734bd2be53bb18f104980a1d Mon Sep 17 00:00:00 2001
From: Vecko <36369090+VeckoTheGecko@users.noreply.github.com>
Date: Mon, 2 Mar 2026 17:42:59 +0100
Subject: [PATCH 3/3] Add TODO

---
 src/parcels/_typing.py | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/parcels/_typing.py b/src/parcels/_typing.py
index 8558cbb5df..3d44281209 100644
--- a/src/parcels/_typing.py
+++ b/src/parcels/_typing.py
@@ -51,9 +51,8 @@ def _validate_against_pure_literal(value, typing_literal):
 
     Can't be used with ``Literal[...] | None`` etc. as its not a pure literal.
     """
-    if _is_xarray_object(
-        value
-    ):  # Xarray objects don't work normally in `in` statements due to https://github.com/pydata/xarray/issues/11209
+    # TODO remove once https://github.com/pydata/xarray/issues/11209 is resolved - Xarray objects don't work normally in `in` statements
+    if _is_xarray_object(value):
         raise ValueError(f"Invalid input type {type(value)}")
 
     if value not in get_args(typing_literal):