check for already existing enum value added; added test (#1453)

* check for already existing enum value added; added test

* added enum value name to exception message

* test for defining enum with multiple identical names moved to test_enum.cpp/py
diff --git a/tests/test_enum.py b/tests/test_enum.py
index c2c272a..a031d95 100644
--- a/tests/test_enum.py
+++ b/tests/test_enum.py
@@ -148,3 +148,9 @@
     m.test_enum_to_uint(m.ClassWithUnscopedEnum.EMode.EFirstMode)
     m.test_enum_to_long_long(m.Flags.Read)
     m.test_enum_to_long_long(m.ClassWithUnscopedEnum.EMode.EFirstMode)
+
+
+def test_duplicate_enum_name():
+    with pytest.raises(ValueError) as excinfo:
+        m.register_bad_enum()
+    assert str(excinfo.value) == "Enum error - element with name: ONE already exists"