add a unit test for pickling and unpickling databases

since `Database` does not provide a comparison operator, we compare
the `repr()` strings of the fresh and the unpickled database.

thanks to [at]kayoub5 for suggesting this.

Signed-off-by: Andreas Lauser <[email protected]>

Author: andlaus

tests/test_pickle_db.py

@@ -0,0 +1,19 @@
+# SPDX-License-Identifier: MIT
+import pickle
+import unittest
+
+from odxtools.loadfile import load_pdx_file
+
+
+class TestPickleDatabase(unittest.TestCase):
+
+    def test_state_chart(self) -> None:
+        fresh_db = load_pdx_file("./examples/somersault.pdx")
+        pickled_db = pickle.dumps(fresh_db)
+        unpickled_db = pickle.loads(pickled_db)
+
+        self.assertEqual(repr(fresh_db), repr(unpickled_db))
+
+
+if __name__ == "__main__":
+    unittest.main()