Your first X++ unit test with SysTest in D365 F&O

An X++ unit test is a class extending SysTestCase, where each test method carries the SysTestMethodAttribute attribute and checks a result with assertions (assertEquals, assertTrue, assertFalse…). You put it in a dedicated test model whose name contains "Test", build, and the tests show up in Visual Studio's Test Explorer, where you run them.

By default, each test runs with AutoRollback isolation: all writes are rolled back at the end, no data persists.

Example adapted from Microsoft Learn (Fleet Management sample app), checking a field validation:

class FMUnitTestSample extends SysTestCase
{
    [SysTestMethodAttribute]
    public void testFMCarValidateField()
    {
        FMCarClass fmCar;

        fmCar.NumberOfDoors = -1;
        this.assertFalse(fmCar.validateField(fieldNum(FMCarClass, NumberOfDoors)));

        fmCar.NumberOfDoors = 4;
        this.assertTrue(fmCar.validateField(fieldNum(FMCarClass, NumberOfDoors)));
    }
}

The setup method lets you prepare data before each test. After saving and building, open Test > Test Explorer, select the test and run it.

The SysTestTransaction attribute picks the isolation: AutoRollback (default, best), LegacyRollback (tracks and deletes inserts; useful for testing user connections or concurrency), LegacyRollbackWithUpdateTracking (slowest), None (debugging only).

[SysTestTransaction(TestTransactionMode::LegacyRollback)]
class MyTestSample extends SysTestCase

Create a separate test model and include "Test" in its name: the default build definition discovers test modules by that name. Two documented caveats: builds on Microsoft-hosted agents do not support running SysTest tests (no runtime); in the unified developer experience (UDE), test code must be deployed to the environment before it runs, and requires Application Foundation and Test Essentials. See UDE: what changes for an X++ developer.

• Writing tests that rely on unprepared existing data: they pass or fail depending on the environment.
• Switching to None isolation and forgetting to switch back: tests leave data behind.
• Mixing test code and application code in the same model.
• Expecting pre/post handlers on a test method: they are not hookable by default (add [Hookable(true)] if needed).
• Relying on the hosted pipeline to run tests: it only compiles and packages.

Unit tests are part of what Skalp delivers with the code. Skalp AI writes the specification, generates the X++ code and unit tests, compiles with a best-practice check, then delivers a pull request to your Azure DevOps: nothing is merged without your technical architect's approval. See AI X++ development, the bigger picture in building X++ without a consultant in 2026, and the Basic, Pro and Max plans (1 credit, ≈ €400 on Basic, €200 on Pro, consumed only when the code is generated).

• Microsoft Learn, "Testing and validations", updated 29 Apr 2026, accessed 18 Oct 2026.
• Microsoft Learn, "Build automation that uses Microsoft-hosted agents and Azure Pipelines", updated 5 Mar 2026, accessed 18 Oct 2026.
• Microsoft Learn, "Unified developer experience - Frequently asked questions", updated 23 Jul 2026, accessed 18 Oct 2026.