Verifying change over versions.
WHY IT IS THE MOST NEGLECTED TESTING
New installations are tested; upgrades are assumed.
WHO IT AFFECTS
Existing users, who have data.
WHAT TO TEST
Upgrading from the currently released version Upgrading from several versions back Upgrading with realistic data volume Upgrading with data in unusual states
WHAT UNUSUAL STATES MEANS
Records created by older versions Incomplete records Data violating constraints added later
WHY THAT LAST ONE MATTERS
Migrations adding constraints fail on existing data that violates them.
WHAT TO VERIFY AFTER UPGRADE
That data is intact That derived values are correct That the application functions That previously configured settings survive
WHAT TO TEST ABOUT FAILURE
Migration interrupted partway.
WHAT TO VERIFY
Whether it can be resumed or reversed.
WHAT TO MEASURE
Duration at production volume.
WHY
A migration taking hours means an outage.
WHAT TO TEST ABOUT ROLLBACK
Returning to the previous version, with data written by the new one.
WHY THAT IS FREQUENTLY IMPOSSIBLE
New data may not fit the old structure.
WHAT TO ESTABLISH
Whether rollback is possible at all, before releasing.
