bcquality/microsoft/knowledge/testing/testisolation-belongs-on-the-test-runner.md
Jesper Schulz-Wedde 2b5550c346
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Improve partner onboarding and documentation navigation (#174)
Lead with a complete plugin quick start and add task-oriented usage, troubleshooting, customization, and contribution guides. Preserve the broader plugin framing, correct conflicting contract guidance, support Agents folder reviews, and align repository validation. Convert existing sample references to clickable links without changing knowledge rules.

Co-authored-by: Jesper Schulz-Wedde <jesper.schulzwedde@microsoft.com>
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
2026-09-09 17:31:03 +02:00

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---
bc-version: [all]
domain: testing
keywords: [testisolation, testrunner, autocommit, commit, rollback, test-order, database-state]
technologies: [al]
countries: [w1]
application-area: [all]
---
# Configure TestIsolation on the test runner
## Description
`TestIsolation` is a property of a `Subtype = TestRunner` codeunit, not of the test codeunit being executed. Its default is `Disabled`. `Codeunit` rolls back database changes after each test codeunit and `Function` after each test method, including changes that the code under test explicitly committed. Without runner isolation, an `AutoCommit` test can leave data behind and make later tests order-dependent.
## Best Practice
Run independent suites with `TestIsolation = Codeunit` or `Function`, choosing the narrowest boundary the runner supports. Pair this with the appropriate method-level `TransactionModel`: `AutoCommit` permits code under test to commit, while runner isolation still restores the database afterward. Keep isolation disabled only for an intentionally shared-state suite whose ordering and cleanup are explicit.
See sample: [`testisolation-belongs-on-the-test-runner.good.al`](testisolation-belongs-on-the-test-runner.good.al).
## Anti Pattern
An `AutoCommit` test exercises committed writes under a test runner that omits `TestIsolation` or sets it to `Disabled`, then assumes the database is restored automatically. This article owns runner-level rollback; `transactionmodel-attribute-governs-test-transactions.md` separately owns the method attribute.
See sample: [`testisolation-belongs-on-the-test-runner.bad.al`](testisolation-belongs-on-the-test-runner.bad.al).