Why testing comes before trust
An automation that is right nine times and quietly wrong the tenth is dangerous, because by then everyone has stopped checking. Testing is how you find the tenth case while the manual process is still there to catch it.
Run both side by side
For a few cycles, which means a few weeks for a weekly task, keep doing the task by hand and let the automation run as well. Compare the two results row by row. Every difference is either a bug in the automation or a rule nobody had written down, and both are worth finding.
Test the awkward cases on purpose
- A record with a missing field, or a date in a different format.
- The same customer or order twice, spelled slightly differently.
- An export with a new column, a renamed column, or no rows at all.
- A file that arrives late, twice, or not at all.
Keep a small folder of these test inputs, and run them again whenever the automation changes.
Check the result, not just the run
A run that finishes without an error is not the same as a correct result. Compare totals with the source, count the rows going in and coming out, and list anything that was skipped. Keep those checks after the testing is over: on a normal day, they are what tells you that something has changed.
Decide what happens when it fails
Before switching the manual process off, agree who is told when the automation fails or a check does not pass, how they are told, and what they do next. An automation that stops quietly is worse than none, because everyone assumes it still works.
Switching over
When the side-by-side results have matched for long enough, and the awkward cases are handled or flagged, switch the manual process off and keep the checks. Every Workflow Fix we deliver includes a check step and handover notes that say what to look at. Our guide on copying data between spreadsheets lists simple checks to start with.