The WildFly 25 moved from jettison dependency of the Rest Easy of version 3.x to JSON-P dependency of version 4.x.
See commit https://github.com/wildfly/wildfly/commit/bf5af29b2885089607694ac122ecb07a2868663c#diff-24473473b04fed199ce35ba61ad0ee9bb12009a6dbadbf9458837ed9d4d2c334L36

As the WildFly removed the Jettison module completely the XTS and RTS tests which run with Arquillian on container fail.

There could be used json api instead of the Jettison.