How to do it...

Perform the following steps:

1. Navigate to the build definition AzureServerlessCookBook-C# Function-CI by clicking on the Edit button as shown in the following screenshot:

2. Once you are in the build definition, click on the Triggers menu, shown as follows:

3. Now, click on the Enable continuous integration checkbox to enable the automated build trigger. 
4. Save the changes by clicking on the arrow mark available beside the Save & queue button and click on the Save button available in the drop-down menu, which is shown in the following screenshot:

5. Let's navigate to the Azure Function project in Visual Studio. Make a small change to the last line of the Run function source code that is shown next. I just replaced the word hello with Automated Build Trigger test by:

return name != null ? (ActionResult)new OkObjectResult($"Automated Build Trigger test by, { name}")
          : new BadRequestObjectResult("Please pass a name on the query string or in the request body");

6. Let's check in the code and commit the changes to the source control. As shown here, you will get a new change set ID generated. In this case, it is Changeset 32:

7. Now, immediately navigate back to the Azure DevOps build definition to see that a new build got triggered automatically and is in progress, as shown in the following screenshot: