Converted test_pickle_message to pytest, and removed reliance on Iris

src/iris_grib/tests/unit/message/test_pickle_message.py

@@ -0,0 +1,48 @@
+# Copyright iris-grib contributors
+#
+# This file is part of iris-grib and is released under the BSD license.
+# See LICENSE in the root of the repository for full licensing details.
+"""Check that a GribMessage can be pickled."""
+
+# Import iris_grib.tests first so that some things can be initialised before
+# importing anything else.
+import iris_grib.tests as tests
+
+import pickle
+
+import pytest
+from iris_grib.message import GribMessage
+
+MIN_PICKLE_PROTOCOL = 4
+
+TESTED_PROTOCOLS = list(range(MIN_PICKLE_PROTOCOL, pickle.HIGHEST_PROTOCOL + 1))
+
+
+@tests.skip_data
+class TestPickleGribMessage:
+    @pytest.fixture
+    def messages(self):
+        path = tests.get_data_path(("GRIB", "fp_units", "hours.grib2"))
+        return GribMessage.messages_from_filename(path)
+
+    def pickle_obj(self, obj, protocol, tmp_path):
+        # NOTE: Neither GribMessage, nor its lazy ".data", read back from
+        # a pickled obj. Currently, this only checks that they can be pickled
+        # successfully.
+        filename = tmp_path / ".pkl"
+        with open(filename, "wb") as f:
+            pickle.dump(obj, f, protocol)
+        # TODO: resolve this or remove the test.
+        #  with open(filename, "rb") as f:
+        #      nobj = pickle.load(f)
+        #  assert nobj == obj
+
+    @pytest.mark.parametrize("protocol", TESTED_PROTOCOLS)
+    def test_message(self, protocol, messages, tmp_path):
+        obj = next(messages)
+        self.pickle_obj(obj, protocol, tmp_path)
+
+    @pytest.mark.parametrize("protocol", TESTED_PROTOCOLS)
+    def test_message_data(self, protocol, messages, tmp_path):
+        obj = next(messages).data
+        self.pickle_obj(obj, protocol, tmp_path)