fix: add deprecation warning in io module

Author: jokasimr

packages/essdiffraction/src/ess/beer/io.py

@@ -3,10 +3,18 @@
 
 """Backward-compatible import location for BEER McStas helpers."""
 
+import warnings
+
 from . import mcstas as _mcstas
 from .mcstas import *  # noqa: F403
 from .mcstas import __all__  # noqa: F401
 
+warnings.warn(
+    "ess.beer.io is deprecated; use ess.beer.mcstas instead.",
+    DeprecationWarning,
+    stacklevel=2,
+)
+
 
 def __getattr__(name: str):
     """Return attributes from the replacement :mod:`ess.beer.mcstas` module."""

packages/essdiffraction/tests/beer/mcstas_reduction_test.py

@@ -1,3 +1,6 @@
+import importlib
+import sys
+
 import numpy as np
 import pytest
 import scipp as sc
@@ -162,9 +165,12 @@ def test_can_load_monitor():
 
 
 def test_io_module_reexports_mcstas_loaders():
-    from ess.beer.io import load_beer_mcstas as load_beer_mcstas_from_io
+    sys.modules.pop('ess.beer.io', None)
+
+    with pytest.warns(DeprecationWarning, match='ess.beer.io'):
+        io = importlib.import_module('ess.beer.io')
 
-    assert load_beer_mcstas_from_io is load_beer_mcstas
+    assert io.load_beer_mcstas is load_beer_mcstas
 
 
 @pytest.mark.parametrize(