How we test
Each workbook release is checked by an independent test suite before it ships. The person who writes the tests works from the product specification and design notes only, and never reads the code that builds the workbook.
Last updated 2026-10-27.
1. Evaluate every formula
We build each release file and evaluate every formula in it with HyperFormula, an open-source spreadsheet engine, so the tests read the same numbers Excel would show. A scan of every non-empty cell must find zero error values and no circular references.
2. Recompute independently
A separate reference engine, written in TypeScript from the specification and anchored to hand-worked cases, recomputes the outputs from the same inputs. The workbook must match it to within 0.01 on every compared figure.
3. Plant errors and watch the checks fail
A check that cannot fail proves nothing. For each check that inputs can break, we plant a known error (an unbalanced trial balance, an IBR of 45%, a missing mapping, an unsigned reconciliation) and confirm that the check shows FAIL and that the overall result turns FALSE.
4. Recalculate in desktop Excel
Each release file is fully recalculated in Excel 365 for Windows, and the Checks tab must show every check as PASS on the sample data.
5. Check the file itself
Every file is checked for macros (none), external links (none) and its document properties. The results go into a written acceptance report for each product and version.
Latest acceptance results
Version 1.0.0, tested 2026-10-27
- Pro at full capacity (250 leases by 360 months): 803,702 formulas evaluated, zero error values.
- 12 sample leases in 3 classes, including a rent-free period, an end-of-term payment and one modification of each remeasuring type: every Results figure matched the independent recompute.
- Hand-worked cases for month-end cut-off, rent-free months, end-of-term amounts, nominal and effective rates, Actual/365 day count and advance-payment modifications, each checked against the built file.
- Planted errors on the right-of-use asset, modification inputs, IBR, required fields, duplicate modifications, register rows and Settings: each made its check FAIL.
- Excel 365 for Windows recalculation of the Lite, Pro and Team files: every check PASS, named results equal to the test engine within 0.00005.
Still to do: Excel 2019, Mac and Google Sheets checks (a Google Sheets copy of Lite is planned).
Version 1.0.0, tested 2026-10-27
- Sample of 3 entities, 50 accounts and 541 trial balance rows with intercompany balances: due dates, tie-outs, flux, the management pack and the cash flow matched the independent recompute.
- The full grid (6,000 trial balance rows, 1,000 accounts, 500 reconciliations) matched the independent recompute.
- Planted errors (an unbalanced entity, a missing account, a duplicate row, a missing Prior TB, a sub-ledger off by 100, a flux breach without a comment, the same preparer and reviewer, an intercompany mismatch, a revenue sign flip): each made its check FAIL.
- Zero error values in 153,829 formulas in the release file.
- Excel 365 for Windows recalculation: every check PASS, including account codes entered as numbers on one sheet and text on the other.
Still to do: Excel 2019, Mac and Google Sheets checks.
Version 1.0.0, tested 2026-10-27
- A hand-worked group and five variants (a fair value uplift, a capital injection, an in-year acquisition, a goodwill impairment, an adjusting entry), loaded into the built file, matched the independent recompute and a values-only CTA hand proof.
- Planted errors (an unbalanced subsidiary, a wrong opening translated equity, an unbalanced adjustment, a wrong opening CTA, an intercompany mismatch, ownership of 120%, an unmapped account, an acquisition after the year end, negative goodwill, impairment above goodwill): each made its check FAIL.
- Zero error values in 39,828 formulas in the Pro release file.
- Excel 365 for Windows recalculation of the Pro and Team files: every check PASS, figures equal to the test engine.
Still to do: Excel 2019, Mac and Google Sheets checks.
What testing does not do
Tests show that the workbook calculates what its design says, on the data we tested. They do not make judgements for you: lease terms, discount rates, control, fair values and materiality stay yours.
This is a tool, not tax, accounting or financial advice. Outputs depend on your inputs and judgement; review them before you rely on them.