The summary.
AUTHORISATION ON INDIVIDUAL RECORDS IS THE COMMONEST SERIOUS INTERFACE FAULT
Authenticate as one user and request another's resource, on every endpoint.
TEST THAT A WEB APPLICATION DOES SOMETHING SENSIBLE WHEN SCRIPTS FAIL TO LOAD
They fail more often than expected, and a blank page is the usual result.
And test double submission — users do click twice, and duplicates are the consequence.
UPGRADE TESTING IS THE MOST NEGLECTED MOBILE GAP
It affects existing users who have data, and a launch failure leaves them with no route to a fix.
FORCE A FAILURE MID-TRANSACTION AND INSPECT THE DATA
That is the only way to verify rollback. And run identical operations concurrently, repeatedly, to catch lost updates.
Migration duration at production volume matters — a migration locking a large table causes an outage.
A SUBSTITUTE DIVERGING FROM THE REAL SERVICE GIVES FALSE CONFIDENCE
Run a small set against the real thing periodically to confirm it still matches.
VERIFY CALCULATIONS BY AN INDEPENDENT METHOD, NOT THE SAME CODE
Wrong numbers look plausible and get acted on. Period boundaries are where the silent errors live.
