bcquality/community/knowledge/testing/use-library-codeunits-for-test-fixtures.md
Jesper Schulz-Wedde 6c02d68b4e Add testing knowledge: UI handlers, table relations, asserterror, fixtures (P1+P2)
Six BC-specific testing-domain knowledge articles in community/knowledge/testing/, each with .good.al/.bad.al samples:

- ui-calls-require-test-handlers
- tablerelation-requires-prerequisite-records
- handlers-enqueue-never-assert
- handlerfunctions-attribute-must-match-ui-path
- asserterror-needs-expectederror-and-code
- use-library-codeunits-for-test-fixtures

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
2026-06-29 16:10:17 +02:00

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---
bc-version: [all]
domain: testing
keywords: [library-codeunits, fixtures, test-data, number-series, prerequisite]
technologies: [al]
countries: [w1]
application-area: [all]
---
# Build fixtures with the test Library codeunits, not hand-rolled Init/Insert
## Description
BC ships a layer of test Library codeunits — `LibrarySales`, `LibraryPurchase`, `LibraryERM`, `LibraryInventory`, `LibraryRandom` and many more — whose job is to create valid records. `CreateCustomer` assigns a number from the customer number series, fills the mandatory fields, and satisfies the table relations the platform enforces; `CreateItem` does the same for items. Hand-rolling `Customer.Init`/`Customer.Insert` with invented values skips the number series and any field a future app version adds as mandatory, so the fixture is invalid the moment it is created and rots silently as the schema evolves. Prefer the Library codeunits for prerequisite data: they encode the setup the platform requires and are maintained alongside the base app.
## Best Practice
Reach for the matching Library codeunit before writing manual record setup: `LibrarySales.CreateCustomer`, `LibrarySales.CreateSalesHeader`/`CreateSalesLine`, `LibraryInventory.CreateItem`, `LibraryERM.CreateGLAccount`, and `LibraryRandom.RandInt`/`RandDec` for values. Pass the records they return into the code under test. The fixtures stay valid across upgrades because the library — not your test — owns the knowledge of what a well-formed record requires.
See sample: `use-library-codeunits-for-test-fixtures.good.al`.
## Anti Pattern
`Customer.Init(); Customer."No." := 'X'; Customer.Insert();` — a record with a hand-picked primary key, no number-series entry, and none of the mandatory fields a real customer needs. It compiles and may even insert, but it bypasses setup the production code assumes, and it breaks the first time the schema gains a required field the test does not know about.
See sample: `use-library-codeunits-for-test-fixtures.bad.al`.