GraphWalker goes through all files in the
src/test/resources folder, and tries to see whether it can work with that file (is it a graphml, json or dot file). It has so called context factories for all these different file extensions.
The above message simply means that it could not find a suitable factory based on the extension of the currently analyzed file.
If it only happens once, this can be ignored as the application has a logback.xml file in the resources folder, and the message says that graphwalker will not handle that file.