MockDataFactory class needs to be defined at Client side i.e., in the Java project only. WmTestSuite internally takes care of transferring and loading the same in server.
In general, if user wants to load classes, code\source is where java types are declared. User can then use jcode utilities for compilation or asset generation. Server implicitly loads classes from code\classes location.
Would recommend having a look at this article around triggering WmTestSuite test cases and derive corresponding maven configuration from there on. Test Suite Executor - Knowledge base - webMethods - Software AG Tech Community & Forums