Advanced ETL Processor has a lot of useful features designed to make the life of Business intelligence consultants easier. One of them is "Magic Button". At any time the user can press it and see the result of data transformation or validation without actually loading the data.
Here is a data sample we want to check if the customer id is numeric and reject it if not
Here is the mapping we will use for it.
And we can immediately see the result of transformation: record rejected
It is also possible to enter the data directly into the source grid and test it the transformation that way