Tax calculation regression: pre-release and first 30 minutes checklists

Tax or VAT is computed with the wrong rate or jurisdiction after a rules or data update.

The pre-release checklist maps each item to a test class from the incident page. The first-30-minutes checklist covers detection, containment, the rollback decision and customer communication.

6 pre-release items · 6 first-30-minutes items · verified 2026-10-21

Pre-release checklist

PR-01Add a unit test that computes the tax amount on each tax report line from the current rate table entry, not from a literal multiplier such as 0.2. unit
PR-02Search tax report formulas for literal rate values and confirm each one matches the current rate table entry for that jurisdiction. unit
PR-03Add a unit test that fails when a tax report line's taxable amount and tax amount use different rates. unit
PR-04Add an integration test that saves a reservation item with a price override and the tax dropdown disabled, then reads the stored tax code back from the database. integration
PR-05Confirm the endpoint that stores tax codes rejects an empty array instead of saving it. integration
PR-06Add an integration test that generates an invoice from a booking with a price override and compares the invoice VAT rate with the rate table entry for that item. integration

First 30 minutes

FM-01Compare the VAT rate on invoices issued since the release with the rate table entry for each affected item.
FM-02Query the database for bookings stored with an empty or invalid tax code since the release and record the count.
FM-03Disable the feature that writes tax codes on overridden prices, or revert the release that introduced it.
FM-04Decide on rollback by checking whether new bookings still receive invalid tax codes after the feature is disabled.
FM-05Write a remediation script for the stored tax codes and run it on a database copy before production.
FM-06Tell affected customers which invoices carry invalid tax information and what guidance applies to them.

Download the checklist

Pre-release checklist (Markdown)1.3 KB · v1.0.0
First 30 minutes checklist (Markdown)1019 B · v1.0.0

Only in this checklist

Every test class in this checklist also appears in at least one sibling checklist in the group; the item texts differ: Add a unit test that computes the tax amount on each tax report line from the current rate table entry, not from a literal multiplier such as 0.2.

Questions

What should be checked before a release to prevent Tax calculation regression?

6 pre-release items, PR-01 to PR-06. PR-01: Add a unit test that computes the tax amount on each tax report line from the current rate table entry, not from a literal multiplier such as 0.2.

Is there a rollback plan for Tax calculation regression?

The first-30-minutes checklist has 6 items. FM-01: Compare the VAT rate on invoices issued since the release with the rate table entry for each affected item.

What should a team do in the first 30 minutes after Tax calculation regression is detected?

The first-30-minutes checklist has 6 items. FM-01: Compare the VAT rate on invoices issued since the release with the rate table entry for each affected item.

Is a Tax calculation regression checklist still needed if deployment is automated?

Yes. Automation runs the steps; the checklist names what the tests must cover: unit tests and integration tests.

Which pipeline stages does the Tax calculation regression checklist cover?

The pre-release items map to the pre-merge and pre-deploy stages.

In what formats can the Tax calculation regression checklist be downloaded?

Both checklists download as Markdown files: /downloads/tax-calculation-regression-pre-release.md and /downloads/tax-calculation-regression-first-30-minutes.md, licensed CC BY 4.0.