ERP implementation must be carefully planned should an organization decide to purchase a complete ERP solution. And UAT or User-Acceptance Testing is one of the most important, if not the top important milestone, in ERP implementation.
Sadly, not all people realize its value. Most of them, even some vendors, skip UAT.
Writing a comprehensive test script is a must right after the business process has been finalized. This should be complete and end-to-end with an agreed data-set as the criteria for acceptance.
Regardless, if there are software code modifications or not, UAT should be executed because you would want to test out configurations, especially if the ERP is highly flexible and robust. Examples of configurations are transaction approval workflow or posting process.
Testing out transactions and reports with a dummy dataset is significantly ineffective compared to testing them using actual strategic sample documents and transactions aligned with the agreed business flow.
In our case, sample transactions can be 5 to 10 actual purchase orders, vouchers, and invoices. Expected results are also important. Make sure journal entries, report schedules, and financial statement results are well defined.
With this process at our side, it is easier for us to manage client expectations by simulating the agreed test scripts and making sure all items passed the QA check prior to software release.
ERP test preparation is a lot of work but I really believe this will shorten the implementation time compared to the trial-and-error approach. The more complete it is, the fewer problems you will encounter when the ERP goes live.