Beautiful Testing

Diamond in the Rough: Testing XML Validity

When testing the functionality of our protocol in the previous sections, we separated the stanza representation from the actual logic of the protocol to improve the focus of our tests. This split made testing the logic of the protocol straightforward and clean. Unfortunately, testing the representational part that converts the abstract stanzas into XML and back is still tedious and error-prone. One of the things that needs to be checked is whether every variation of the payload transforms correctly to a standards-compliant XML element. For example, for the version payload we used earlier, we need to test the representation of a payload with and without a version number. Conversely, the transformation from XML to a payload data structure needs to be tested for every possible compliant XML element. It would be handy if we could automatically check whether our XML parser and serializer handles all of the possible variations of payloads and stanzas allowed by the protocol standard.

A possible approach for testing XML parsers and serializers is automated XML validation. Every protocol specification published by the XMPP Standards Foundation comes with an XML schema. This schema describes the syntax and constraints of the XML used in the protocol. For example, it specifies the names of the XML elements that can occur in the payload, the names and types of the attributes of these elements, the number of times an element can occur, and so on. Such ...