What problem does it solve? Upgrading MSTest packages from 3.x to 4.x breaks builds with errors like CS0507, CS0103, and CS1061, and introduces silent behavioral changes such as lost test discovery and altered TestCase.Id generation. This Skill diagnoses those errors and walks through every source-incompatible and behavioral change until the project builds cleanly and all tests pass. ## Core Features & Use Cases - Breaking change resolution: Maps compiler errors to concrete fixes, including Execute to ExecuteAsync, CallerInfo constructors on TestMethodAttribute, ClassCleanupBehavior removal, TestContext.Properties ContainsKey, and Assert.ThrowsException to ThrowsExactly. - Behavioral change guidance: Addresses TestCase.Id regeneration, TreatDiscoveryWarningsAsErrors defaults, AppDomain changes, and MSTest.Sdk MTP mode versus vstest.console compatibility. - Use Case: After bumping MSTest.TestFramework to 4.1.0, your build fails on a custom TestMethodAttribute subclass and [ExpectedException] usages. The Skill identifies each error, provides copy-pasteable fixed code, and verifies the migration with dotnet build and dotnet test. ## Quick Start Migrate my test project to MSTest v4 and fix all the build errors that appeared after updating the packages.
