Part 6 · 1 chapters · ~10 min
Verification and Validation
Verification against the specification and validation against the need: the V model pairing design levels with test levels, four verification methods, validation with real users, traceability in both directions, a test strategy by level, and an evidence pack for the clearance letter.
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Built right, and the right thing
| requirement (clearance letter) | method | evidence |
|---|---|---|
| R1 a letter is issued only when the outstanding balance is zero at generation time | test | unit tests on the rule; integration test against a ledger fixture with a 1-kobo balance |
| R2 generated within 60 s at p99 under month-end peak load | test | load test at 3× average daily rate in staging; report attached |
| R3 every letter is verifiable by the receiving party | demonstration | QR verification shown to two partner banks in the pilot |
| R4 signing keys never leave the HSM | inspection | architecture and IAM review signed by security |
| R5 the letter is accessible (WCAG 2.2 AA) as a tagged PDF and on screen | test + inspection | axe on the page; PDF/UA checker on samples; screen reader pass |
| N1 customers can get a letter without contacting support | validation | pilot: support contacts for letters before and after |
validation is where staff engineers earn trust
Verification is a team habit; validation needs someone to ask whether the thing worked for the people it was for, and to go and find out. For the letter, the measure that matters is the monthly count of manual support issues, which started at 249.
VERIFICATION AND VALIDATION
did we build it right, did we build the right thing, and the V that pairs every level of design with a level of test
swipe the figure sideways, or tap expand for full screen
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the V
The V: down the left side, needs become requirements, requirements become an architecture, the architecture becomes component designs, and code is written at the bottom. Up the right side, each level is checked against its partner on the left. A defect found on the right is traced back to the left-hand level where it was introduced.