Add explicit test for casing rules

Author: boukeversteegh

betterproto/tests/inputs/casing/test_casing.py

@@ -0,0 +1,16 @@
+import betterproto.tests.output_betterproto.casing.casing as casing
+from betterproto.tests.output_betterproto.casing.casing import Test
+
+
+def test_message_attributes():
+    message = Test()
+    assert hasattr(message, 'snake_case_message'), 'snake_case field name is same in python'
+    assert hasattr(message, 'camel_case'), 'CamelCase field is snake_case in python'
+
+
+def test_message_casing():
+    assert hasattr(casing, 'SnakeCaseMessage'), 'snake_case Message name is converted to CamelCase in python'
+
+
+def test_enum_casing():
+    assert hasattr(casing, 'MyEnum'), 'snake_case Enum name is converted to CamelCase in python'