In our company, we use XML as a core part of the integration. We had a few occasions where our customer raised the concern that our XML's are not validated as per the schema. I have asked the QA team to include XML schema validation as part of their testing. They resisted taking new responsibility saying that only developers need to do the schema validation as XSD files are code and therefore it is not part of their QA testing.
My argument would be if developer misses the XML schema validation then QA will catch it before it goes on Live. Similar to UI form data validation XML is data that needs to be validated against its schema, and therefore both developers and testers need to take the responsibility.
Please, can you confirm what would be the norm as per industry standards, who should validate XML code against the schema?