The summary.
TEST ON THE OLDEST SUPPORTED BROWSER AND DEVICE
That is where features silently fail. And test with content blockers enabled, since they are widely used and can break functionality entirely.
PSEUDO-LOCALISATION FINDS UNTRANSLATED STRINGS AND LAYOUT BREAKAGE WITHOUT TRANSLATIONS
And date order differences produce wrong values that look perfectly valid.
IN PAYMENT FLOWS, EVERYTHING EXCEPT SUCCESS IS COMMONLY UNTESTED
The failure paths are where money is lost. Test the unknown outcome specifically, and verify records stay consistent after every case.
NEVER POINT A TEST ENVIRONMENT AT REAL MAIL DELIVERY
And check that message links point at the right environment — production links in test mail is a common, damaging error.
SEARCH AND EXPORTS ARE THE COMMON ROUTES TO EXPOSING DATA THE INTERFACE HIDES
Verify permission filtering in both, and enforce tenant scoping at the data layer rather than the interface.
UPGRADE TESTING IS THE MOST NEGLECTED AREA IN ALL OF TESTING
New installations get tested; upgrades get assumed. Test with realistic volume, old data states, and interruption — and establish whether rollback is possible at all before releasing.
