Test and validate your functions with Develop mode in Fabric User Data Functions (Preview)
We’ve made a major update to User Data Functions! This update addresses the most critical feedback we have received since the start of the preview: the testing and development experience of your functions.
Important note: In order to use this feature, you need to upgrade to the latest version of the fabric-user-data-functions library.
Beginning in August, the Functions explorer in the Fabric portal will now use two different modes to interact with your functions: Develop mode and Run/View only mode. These modes provide a dedicated space for users with different permissions to perform their tasks.
- Develop mode allows users with Write permissions to use the portal editor to view, edit, test and publish the code. The Test capability lets you execute your functions in a dedicated environment before publishing them, allowing you to get immediate outputs and logs for your code changes. You can also view your modified code here, separate from the published code in Run only mode.
- Run only mode allows users with Execute permissions to view and execute the published version your functions. This mode will also show a read-only version of the published code without showing any of the changes that have not been published yet.
- View only mode shows a read-only version of the code and its metadata. This mode is visible for users who only have Read permissions to the User Data Functions item. If a user has Execute permissions, they will see the Run only mode instead.
Testing your functions in Develop mode
One key feature of Develop mode is the Test capability. This feature allows you to execute your functions in a separate environment without having to publish them. You can make real-time changes to your code and view their outputs, logs and errors immediately. Once you have completed the changes you need, you can publish your functions and make them available for any user to run them.
To use this feature, first access the Develop mode, and then click on the Test icon in the Functions explorer list. This will open a side panel where you can use the Test button to start a test session. This session will allow you to execute your functions in their current state. You can test any function in the Functions explorer, including newly added functions.
Important note: In order to use this feature, you need to upgrade to the latest version of the fabric-user-data-functions library.
What exactly is a test session and how is it reported?
A test session is a live Python runtime used to read and run your current code changes. This runtime will use the code from your code editor, the libraries you installed in the Library Management experience and the connections you created in the Manage Connections experience.
The session starts when you test your functions for the first time and it has a timeout of 15 minutes that is extended with every execution. Once it starts, you can use it to test any functions.
The total length of the test session is reported against your capacity as CU/s under the User Data Functions Portal Test operation name. You can learn more about this by visiting the Fabric operations documentation.
UPDATE: The capacity usage for the User Data Functions Portal Test operation will begin on October 27th, 2025. Please review the Fabric operations documentation article to learn more.
Get started
If you already have User Data Functions created, you may need to update your fabric-user-data-functions library to the latest version. To update this library, follow these steps:
- Select Library Management from the Functions portal page.
- Locate the
fabric-user-data-functionslibrary in the table, hover over it and select the edit icon. - Select the latest version from the from the dropdown; it’s listed at the top. There’s no need to publish your functions after updating your library. It’s always a good idea to keep this library up to date.
Important note about region availability
The Test capability is not available in all Fabric regions yet. Region support will be incrementally added. If your Tenant region is not supported yet, you may find the following message in the Functions portal.
If this informational message populates, you can still publish your functions and use the Run capability to test them as you did before.
Learn more about how to manage your Fabric capacity if you prefer to create a new capacity in one of the supported regions.
Resources
Feel free to email FabricUserDataFunctionsPreview@service.microsoft.com if you have any more questions.
To learn more about the new features and Fabric User Data Functions, refer to the following documentation.
- Read the documentation of Develop mode in the Microsoft Fabric docs.
- Learn more about Fabric User Data Functions in the Microsoft Fabric docs.
