Test Execution with Hot Reload

Test runs in Visual Studio involve building the project to update the binaries on disk before using Test Platform to execute your tests. The build time inside Visual Studio can vary depending on the kind of changes made to the code. For larger solutions, builds can be the most expensive part of the test run.

In Visual Studio 2022 and later, test execution with hot reload can be enabled to speed up test execution by skipping builds for supported scenarios.

What is supported?

• C# and VB projects targeting .NET 6.0 and later
• Test projects built for the DEBUG configuration
• Visual Studio 2022 and later

Enable Test Execution with Hot Reload

Why is it Experimental?

This feature provides a new approach for test execution that changes a widely used path for validating code. The user experience for this feature can change as we continue to receive feedback. For these reasons, the feature is currently labeled as "experimental."

How it works

After the option is enabled, Test Explorer automatically uses test execution with hot reload when possible. If a hot reload isn't possible, it falls back to the regular behavior of building and running tests. As a user running tests, you don't need to make any changes to your workflow (that is, continue to edit code and run tests).

Under the hood, we're using the same Edit and Continue infrastructure that exists in the newly released Hot Reload experience for editing C#/VB code at runtime to determine the changes made. For this reason, we hot reload only when there are no "rude edits", in which case we fall back to building your tests before executing them. For more details on supported edits, read the Edit and Continue documentation

How much faster is test execution?

There are many variables that come into play when estimating how much time this feature saves you. For example:

• How long the project build takes.
• What kind of edit was made.
• How large the file is where the edit was made.
• Where the edit was made (if it was a leaf project or not).

Ultimately, the speed improvements are directly related to the build time that would have occurred in that specific test run.

Notes

• The first test run after enabling the option or opening Visual Studio triggers a project build.

• Files in the editor might not be saved when tests are run. To resolve these and before you check in, make sure you do a full build (Ctrl+Shift+B).

• The binaries on disk aren't updated when hot reloaded test execution occurs.

• Hot reloaded test execution doesn't work with "Test > Run All Tests", "Run All Tests in View" in Test Explorer, nor does it work with Run All Tests from the solution node in Solution Explorer. The feature doesn't work with these commands because they currently guarantee building the entire solution.

• When tests with unsupported target frameworks (lower than .NET 6.0) run, a project build occurs.

• If you see any inconsistencies between what's on disk and what Test Explorer shows, try a solution/project build with the Ctrl + Shift + B keyboard shortcut and then run tests. Any explicit build replaces the hot reload test results with the regular full-build test results.

Known issues

Test execution with hot reload doesn't occur in the following scenarios:

• Code Coverage
• Live Unit Testing
• Profiling
• Debugging

Stack traces might not be readable with the presence of unreadable tokens. This issue is being tracked here and is planned for a fix in .NET 7.0.

• The recommended workaround in this case is to build your project and rerun the test.

Your feedback matters

For this experimental feature to be complete, we require your feedback. If you have a suggestion to improve the experience, or encounter any problems, take a moment to provide your input. Only with your feedback can we ensure that critical problems are resolved, and future decisions are prioritized based on your input.

To send feedback, use the Visual Studio feedback mechanism.