We build a resource management app for Jira on Atlassian Forge — capacity planning, timesheets, and invoice export. That last one is the scary part. When your app produces an invoice, a bug isn't a cosmetic glitch. It's a customer billing the wrong number.
Over the past few months we ran a hard QA pass on our own product, focused almost entirely on the XLSX export path. Here are four bugs we found, in the order that we understood them. None of them threw an exception. Every single one produced a file that looked completely fine.
1. Every date happened at the same time of day
Date-only fields in the exported workbook — dates with no time semantics whatsoever — came out carrying an identical time component on every single row. Same timestamp, every row, both sheets.
The dates rendered correctly. Excel showed the right day. But underneath, every value was a fractional serial, and that meant:
