parser: ensure prefix is separated when traversing (#353)

tests/inputs/casing_inner_class/test_casing_inner_class.py

@@ -0,0 +1,14 @@
+import tests.output_betterproto.casing_inner_class as casing_inner_class
+
+
+def test_message_casing_inner_class_name():
+    assert hasattr(
+        casing_inner_class, "TestInnerClass"
+    ), "Inline defined Message is correctly converted to CamelCase"
+
+
+def test_message_casing_inner_class_attributes():
+    message = casing_inner_class.Test()
+    assert hasattr(
+        message.inner, "old_exp"
+    ), "Inline defined Message attribute is snake_case"