added python bindings test for mutable object conversion

tests/unittests/CMakeLists.txt

@@ -94,3 +94,7 @@ else()
         PODIO_SIOBLOCK_PATH=${CMAKE_CURRENT_BINARY_DIR}
   )
 endif()
+
+add_test(NAME unittest.py COMMAND python3 ${CMAKE_CURRENT_SOURCE_DIR}/unittests.py)
+PODIO_SET_TEST_ENV(unittest.py)
+set_tests_properties(unittest.py PROPERTIES WORKING_DIRECTORY ${PROJECT_BINARY_DIR}/tests)

tests/unittests/unittests.py

@@ -0,0 +1,36 @@
+import unittest
+import ROOT
+
+res = ROOT.gSystem.Load("libTestDataModel.so")
+if res < 0:
+    raise RuntimeError("Failed to load libTestDataModel.so")
+
+from ROOT import MutableExampleMC
+from ROOT import ExampleMCCollection
+
+
+class Test_ObjectConversions(unittest.TestCase):
+    def test_conversion_mutable_to_immutable(self):
+        ROOT.gInterpreter.Declare(
+            """
+            void test_accepts_immutable(ExampleMC) {}
+            """
+        )
+        accepts_immutable = ROOT.test_accepts_immutable
+        mutable_obj = MutableExampleMC()
+        accepts_immutable(mutable_obj)
+
+
+class Test_OneToManyRelations(unittest.TestCase):
+    def test_add(self):
+        particles = ExampleMCCollection()
+        parent_particle = particles.create()
+        daughter_particle = particles.create()
+
+        self.assertEqual(len(daughter_particle.parents()), 0)
+        daughter_particle.addparents(parent_particle)
+        self.assertEqual(len(daughter_particle.parents()), 1)
+
+
+if __name__ == "__main__":
+    unittest.main()