If your flow is using a Data Partition (creating Train, Validate) node that is downstream from Drop, Filter, and Transform Variables nodes, and if you also want to include a separately defined Test data source, then the answer about where to include the Test data source depends on the degree to which the Test data source is already prepared. There are several moving parts that can affect the answer.
If you want some assistance about debugging a specific flow, you might be best served by sending a model package to technical support. Here is a link that you can use to open a track, and then send your model package.
https://support.sas.com/en/technical-support.html
This note tells how to create a model package. It also tells about how to work around a server error. (A model package does not include your data.)
46764 - Creating a model package (.SPK file) in SAS® Enterprise Miner(tm)
http://support.sas.com/kb/46/764.html