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title: "AL Runner: Testing Against Real Cronus Data, Debugging Restored, and Mutation-Ready Coverage"
summary: "AL Runner, an in-memory test runner for Business Central AL code, gained several capabilities through v2.10.0: a --test-data flag that loads real Cronus demo rows from the BC backup, restored breakpoint debugging via a Debug Adapter Protocol server, per-test coverage for mutation testing, and TDD mode that now works with watch. v2.8.0 also makes compilation fail whenever the BC compiler reports an error."
tier: community
language: en
tags:
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  - code quality
  - mutation testing
  - al runner
  - tdd
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system: development
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    url: https://stefanmaron.com/posts/al-runner-tests-against-cronus/
    title: "AL Runner: Testing Against Real Cronus Data, Debugging Restored, and Mutation-Ready Coverage"
    date: "2026-09-01"
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post_id: https://stefanmaron.com/posts/al-runner-tests-against-cronus/
source_id: stefanmaron-com
source_name: Stefan Maron
url: https://stefanmaron.com/posts/al-runner-tests-against-cronus/
published_at: "2026-09-01T16:30:00.000Z"
author: Stefan Maron
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words: 1615
quotes: []
code_objects_mentioned:
  - other AL Runner
  - other bcdb
  - other ALchemist
  - other LethAL
systems:
  - development
  - platform
versions_mentioned:
  - 2.10.0
  - 2.8.0
  - "2.2"
  - "2.3"
  - "28.1"
  - "27.5"
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---

# AL Runner: Testing Against Real Cronus Data, Debugging Restored, and Mutation-Ready Coverage

[Read the post](https://stefanmaron.com/posts/al-runner-tests-against-cronus/) · Stefan Maron (Stefan Maron, MVP) · 2026-09-01 · 1615 words · tier community · reviewed (checked by Opus)

> AL Runner, an in-memory test runner for Business Central AL code, gained several capabilities through v2.10.0: a --test-data flag that loads real Cronus demo rows from the BC backup, restored breakpoint debugging via a Debug Adapter Protocol server, per-test coverage for mutation testing, and TDD mode that now works with watch. v2.8.0 also makes compilation fail whenever the BC compiler reports an error.

## Key points

- The --test-data flag fills the in-memory database from the Cronus backup in the BC artifact cache. On BC 28.1 W1 that is 344 tables and 39,231 rows, so tests can catch bugs that depend on setup data.
- --dap brings back breakpoint debugging with per-statement stepping, using the same statement hook as coverage, and offers both TCP and stdio transports.
- A new perTestCoverage field (v2.8.0) shows which statements each test executed. Mutation tools such as LethAL can then run each mutant only against the tests that touched the changed line, instead of the full suite, which took about five hours in one measured run.
- --tdd turns tests that reference missing symbols into failed tests with a diagnostic, can generate stubs for signatures it can infer, and now works together with --watch.
- Behavior change in v2.8.0: compilation stops with exit code 3 on any compiler error, matching what a real BC service tier would refuse to publish.

## AL objects mentioned

As named in the post. A name that matches one object page by exact type and name links to it; the others stay as named.

- other "AL Runner"
- other "bcdb"
- other "ALchemist"
- other "LethAL"

## Context

- Features: Real Cronus data testing, Breakpoint debugging with Debug Adapter Protocol, Per-test coverage attribution, Mutation testing support, TDD mode, Watch mode with TDD, Localized demo data via --country, NumberSequence support
- Versions: 2.10.0, 2.8.0, 2.2, 2.3, 28.1, 27.5

Source: Stefan Maron, community blog. Summary, key points and quotes are derived (CONTENT-NOTICE.md); read the original for the full text.