Fix test that loads realistic GRIB file (#2665)

Author: schlunma

doc/develop/preprocessor_function.rst

@@ -244,12 +244,13 @@ and add the following content:
     """Test function `esmvalcore.preprocessor.example_preprocessor_function`."""
     from pathlib import Path
 
-    import esmvaltool_sample_data
     import iris
     import pytest
 
     from esmvalcore.preprocessor import example_preprocessor_function
 
+    esmvaltool_sample_data = pytest.importorskip("esmvaltool_sample_data")
+
 
     @pytest.mark.use_sample_data
     def test_example_preprocessor_function():

tests/integration/preprocessor/_io/test_load.py

@@ -4,14 +4,14 @@
 import tempfile
 import unittest
 import warnings
+from importlib.resources import files as importlib_files
 from pathlib import Path
 
 import iris
 import numpy as np
 from iris.coords import DimCoord
 from iris.cube import Cube, CubeList
 
-import esmvalcore
 from esmvalcore.preprocessor._io import load
 
 
@@ -56,12 +56,11 @@ def test_load(self):
 
     def test_load_grib(self):
         """Test loading a grib file."""
-        grib_path = Path(
-            Path(esmvalcore.__file__).parents[1],
-            "tests",
-            "sample_data",
-            "iris-sample-data",
-            "polar_stereo.grib2",
+        grib_path = (
+            Path(importlib_files("tests"))
+            / "sample_data"
+            / "iris-sample-data"
+            / "polar_stereo.grib2"
         )
         cubes = load(grib_path)