An iPad is a Mac
Two things I shipped in BariCare without checking them, and the check I run now.
A fingerprint icon for Android was built by working out SVG translate and scale values by hand. I shipped it without rendering it. The badge overlapped the fingerprint's own ink and read as an unexplained circle.
The fix was to rasterize the SVG and look at the picture before placing anything. It is a five minute step, and it was the one I skipped.
The second bug labelled a device "Touch ID" because navigator.platform contained "mac". Every iPad since iPadOS 13 reports itself as a Mac, so the check could not tell an iPad from a laptop. The standard way to tell them apart is navigator.maxTouchPoints, and I should have searched for it before writing platform detection.
The client found both on a real device. The rule I keep now: look at the rendered result before calling an interface done, and check a claim about a device API against its documentation before relying on it. A passing typecheck is not evidence that a picture is right.