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migrate-mstest-v3-to-v4

Use this skill before answering, planning, or editing any MSTest 3.x-to-4.x upgrade or post-upgrade failure. Triggers include "MSTest v4 breaking changes"; CS0507/CS0103/CS1061/CS1615; ExecuteAsync, CallerInfo, DisplayName, or custom TestMethodAttribute; ClassCleanupBehavior; ContainsKey; ThrowsExactly or ExpectedException; IsInstanceOfType out parameters; TestTimeout.Infinite; ManagedType; net6/net7 compatibility; TestCase.Id history; TestName in ClassInitialize; TreatDiscoveryWarningsAsErrors; discovery errors after a clean build; and MSTest.Sdk/MTP or vstest.console discovery changes. Do not use for v1/v2-to-v3 leftovers, framework conversion, runner-only migration, or a general .NET upgrade.

plugins/dotnet-test-migration/skills/migrate-mstest-v3-to-v4/SKILL.md

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# MSTest v3 -> v4 Migration

Migrate a test project from MSTest v3 to MSTest v4. The outcome is a project using MSTest v4 that builds cleanly, passes tests, and accounts for every source-incompatible and behavioral change. MSTest v4 is **not binary compatible** with MSTest v3 -- any library compiled against v3 must be recompiled against v4.

## First Action

Inspect the supplied project and source before searching the web or answering
from memory. Classify the request as a focused source fix, runtime behavior
change, CI discovery issue, compatibility question, or full migration, then
follow the matching row below. A clean compile does not exclude this skill:
discovery failures, `TestContext` lifecycle exceptions, and test-history
changes are runtime migration failures.

## When to Use