MSTest v1/v2 -> v3 Migration

Migrate a test project from MSTest v1 (assembly references) or MSTest v2 (NuGet 1.x-2.x) to MSTest v3. MSTest v3 is not binary compatible with v1/v2 -- libraries compiled against v1/v2 must be recompiled.

When to Use

• Project references Microsoft.VisualStudio.QualityTools.UnitTestFramework.dll (MSTest v1)
• Project uses MSTest.TestFramework / MSTest.TestAdapter NuGet 1.x or 2.x
• Resolving build errors after updating MSTest packages from v1/v2 to v3 -- including when the packages already read 3.x and only the source or settings still need fixing
• Replacing .testsettings with .runsettings
• Adopting MSTest.Sdk or in-assembly parallel execution

When Not to Use

• Project already on MSTest v3 with no migration-related build errors and no leftover .testsettings / <LegacySettings> (fully migrated)
• Upgrading v3 to v4 -- use migrate-mstest-v3-to-v4
• Migrating between frameworks (MSTest to xUnit/NUnit)

Boundary Gate

Check package versions before any edit. If all MSTest references are already 3.x, no v1/v2-to-v3 error is reported, and no .testsettings or <LegacySettings> remains, state that migration is complete and make no changes. A 3.x package version alone does not end the migration -- leftover v1/v2-era settings files or breaking-change errors are still in scope. Do not consolidate working v3 packages into the metapackage. Run the existing tests only if verification was requested. This overrides all steps below.

Inputs

Never open by asking for the project path. A user describing their project in prose is asking a question, not withholding a file -- look on disk first. If there is genuinely no project file, answer for the setup they described rather than replying with only a question.

Open the paths exactly as the search returned them. A glob that answers ./TestProject.csproj means the file is there, relative to the working directory -- read it at that path. Do not rebuild it into an absolute path under this skill's own base directory: that directory holds SKILL.md, not the user's project, so the read fails and the project looks missing when it is not. If a file you just found fails to open, the path you constructed is wrong -- retry with the literal result. Never conclude "there is no project on disk" while a search is still reporting project files, and never scaffold a substitute project from the prose description as a workaround.

Breaking Changes Summary

MSTest v3 introduces these breaking changes from v1/v2. Address only the ones relevant to the project:

Response Guidelines

• Always identify the current version first: Before recommending any migration steps, explicitly state the current MSTest version detected in the project (e.g., "Your project uses MSTest v2 (2.2.10)" or "This is an MSTest v1 project using QualityTools assembly references"). This grounds the migration advice and confirms you've read the project files.
• Require project evidence, but gather it yourself: Do not assume v1/v2 from the wording alone -- read the project or central package files and classify the source as QualityTools/v1, NuGet 1.x, or NuGet 2.x. Gather that evidence from the working directory rather than asking the user for it. If the project is already on v3+ with no v1/v2 leftovers, stop and route to the appropriate skill.
• Preserve the test platform: Keep VSTest or MTP unchanged during the framework upgrade unless the user separately requests a runner migration.
• Execute full migrations: When the user asks you to migrate or upgrade the project, edit the files, build, and run tests. Do not stop after listing breaking changes. Advice-only responses are appropriate only when the user asks what to expect.
• Focused fix requests (user has specific compilation errors after upgrading): Address only the relevant breaking change from the table above. Show a concise before/after fix. Do not walk through the full migration workflow.
• DataRow fix requests: Compare every supplied DataRow with its method signature. Mismatches can build with only MSTEST0014 and fail during test execution. Preserve the method contract and normally fix the literal (1L -> 1 for int), then run the affected tests. Change only the rows that are actually wrong. Argument count is not itself a defect on 3.0.3+, so leave a long row alone unless the compiler rejects it.
• Change nothing on suspicion -- confirm the error first: When you believe a construct is unsupported, build and read the actual diagnostic before editing it. If it compiles, this version supports it and it needs no change. Rewriting valid code to dodge a limit the project is not subject to is a defect, not caution.
• Specific feature migration (user asks about one aspect like .testsettings, DataRow, or assertions): Address only that feature, but handle every active setting or affected usage in the supplied files. For .testsettings, put all MSTest settings under one <MSTest> element, map requested deployment, per-test timeout, data collector, and other active configuration, and do not add a session-wide timeout. Do not walk through unrelated breaking changes.
• "What to expect" questions (user asks about breaking changes before upgrading): First state the concrete package update needed to reach v3, then summarize every category in the Breaking Changes Summary, marking which ones directly apply to the visible project. Keep each item to one line and do not expand into release-note history.
• Full migration requests (user wants complete migration): Follow the complete workflow below.
• Comparison questions (user asks about v1 vs v2 differences): Explain concisely -- v1 uses assembly references and requires removing them first; v2 uses NuGet and just needs a version bump. Both converge on the same v3 packages and breaking changes.
• Keep execution project-specific: For fixes and full migrations, change only patterns found in the visible code/configuration. Broader coverage is reserved for explicit "what should I expect?" questions.

Migration Paths

• MSTest v1 (assembly reference to QualityTools): Remove the assembly reference (Step 2), add v3 NuGet packages (Step 3), fix breaking changes (Step 5).
• MSTest v2 (NuGet packages 1.x-2.x): Update package versions to 3.x (Step 3), fix breaking changes (Step 5). No assembly reference removal needed.

Both paths converge at Step 3 -- the same v3 packages and breaking changes apply regardless of starting version.

Workflow

Step 1: Assess the project

1. Locate the project first: glob the working directory for *.csproj, *.sln, *.slnx, Directory.Build.props, Directory.Packages.props, and *.testsettings. Do this before asking the user anything, and open whatever it returns at exactly the path it reported (see the note under Inputs).
2. In one discovery pass, batch-read project and central configuration files, search for affected APIs/settings, and identify which MSTest version is currently in use:
   • Assembly reference: Look for Microsoft.VisualStudio.QualityTools.UnitTestFramework in project references -> MSTest v1
   • NuGet packages: Check MSTest.TestFramework and MSTest.TestAdapter package versions -> v1 if 1.x, v2 if 2.x
3. Check whether the target framework is dropped in v3 (see Step 4).
4. Run the existing test command. Record discovered, passed, failed, and skipped counts as the parity baseline.

Step 2: Remove v1 assembly references (if applicable)

If the project uses MSTest v1 via assembly references:

1. Remove the reference to Microsoft.VisualStudio.QualityTools.UnitTestFramework.dll
   • In SDK-style projects, remove the <Reference> element from the .csproj
   • In non-SDK-style projects, remove via Visual Studio Solution Explorer -> References -> right-click -> Remove
2. Save the project file

Step 3: Update packages to MSTest v3

Use one package model; do not leave duplicate framework/adapter references.

Default -- install the MSTest metapackage:

Remove individual MSTest.TestFramework and MSTest.TestAdapter package references and replace with the unified MSTest metapackage:

<PackageReference Include="MSTest" Version="3.8.0" />

Keep Microsoft.NET.Test.Sdk when the project remains on VSTest, but update it to a version compatible with the selected MSTest release. For example, MSTest 3.8.0 requires Microsoft.NET.Test.Sdk 17.13.0 or later; leaving an older explicit version causes NU1605. If package versions are centrally managed, update Directory.Packages.props rather than adding inline versions.

Use MSTest.Sdk only when the user requests it or the repository already standardizes on it (SDK-style projects only):

Change <Project Sdk="Microsoft.NET.Sdk"> to <Project Sdk="MSTest.Sdk/3.8.0">. MSTest.Sdk automatically provides the MSTest framework, adapter, and analyzers.

Important: MSTest.Sdk defaults to Microsoft.Testing.Platform (MTP). When preserving VSTest, set <UseVSTest>true</UseVSTest>; the SDK then supplies the required Microsoft.NET.Test.Sdk reference. Do not switch runners merely as a side effect of the framework upgrade.

When switching to MSTest.Sdk, remove these (SDK provides them automatically):

• Packages: MSTest, MSTest.TestFramework, MSTest.TestAdapter, MSTest.Analyzers, Microsoft.NET.Test.Sdk
• Properties: <EnableMSTestRunner>, <OutputType>Exe</OutputType>, <IsPackable>false</IsPackable>, <IsTestProject>true</IsTestProject>

Step 4: Update target frameworks if needed

MSTest v3 supports .NET 6+, .NET Core 3.1, .NET Framework 4.6.2+, .NET Standard 2.0, UWP 16299+, and WinUI 18362+. .NET Core 3.1 is end-of-life but remains supported by MSTest v3; preserve it during this framework-only migration and recommend a separate runtime upgrade. If the project targets a framework version dropped by MSTest v3, update to a supported one:

Note: .NET 6, .NET 8, and .NET 9 are all supported by MSTest v3. Do not change TFMs that are already supported.

Step 5: Resolve build errors and breaking changes

Search the supplied files first and fix only breaking changes that are present. A successful build does not prove compatibility; some failures surface only as analyzer warnings or during test execution.

Assertion overloads -- MSTest v3 replaced Assert.AreEqual(object, object) and AreNotEqual(object, object) with the generic AreEqual<T>(T?, T?). This breaks only where T can no longer be inferred, which the compiler reports as CS0411 (or CS1503 for unrelated argument types):

// Breaks -- string and int have no common inferred type:
Assert.AreEqual(referenceCode, numericId);   // CS0411
// Fix -- name the type argument explicitly:
Assert.AreEqual<object>(referenceCode, numericId);

Two object-typed arguments still infer T = object and compile untouched, as do ordinary typed assertions like Assert.AreEqual("A-3", order.Reference). Fix only the call sites the compiler rejects. Widening every assertion in the file to <object> also compiles, so nothing will flag it -- but it discards the type checking v3 added, which is the entire point of the change.

DataRow strict type matching -- argument types must match parameter types exactly. This is not a compile error: the row builds (with MSTEST0014) and fails at run time with "Test data doesn't match method parameters".

// Fails at run time: 1L (long) does not bind to an int parameter -> use 1
// Fails at run time: 1.0 (double) does not bind to a float parameter -> use 1.0f
// Still binds: 1 (int) to a long parameter -- widening conversions are accepted

Preserve method parameter types unless independently wrong. dotnet build may succeed with MSTEST0014; run the test to prove each row binds and executes.

Rows with more than 16 arguments -- leave them alone unless the compiler actually emits CS1729. The cap existed only in 3.0.1/3.0.2 (removed in 3.0.3), so wrapping extras in an object[], casting to object, or splitting the method just rewrites a correct test.

Timeout behavior -- unified across .NET Core and .NET Framework. Verify [Timeout] values still work.

Step 6: Replace .testsettings with .runsettings

The .testsettings file and <LegacySettings> are no longer supported in MSTest v3. Delete the .testsettings file and create a .runsettings file -- do not keep both. Consolidate all MSTest configuration under one <MSTest> element; do not create an <MSTestV2> section.

Key mappings:

Important: Map timeout to <MSTest><TestTimeout> (per-test), not <TestSessionTimeout> (session-wide). Remove <LegacySettings> entirely.

Step 7: Verify

1. Run the same test command, filter, and configuration used for the baseline. dotnet test builds by default; run a separate build only to isolate a compilation failure.
2. Compare discovered, passed, failed, and skipped counts to the pre-migration baseline.
3. Investigate every count difference; do not accept silently dropped tests or data rows.
4. Confirm no QualityTools reference, 1.x/2.x MSTest package, .testsettings, or <LegacySettings> remains.

Validation

• MSTest v3 packages (or MSTest.Sdk) correctly referenced; v1/v2 references removed
• Project builds with zero errors
• All tests pass (dotnet test) -- compare pass/fail counts to pre-migration baseline
• .testsettings replaced with .runsettings (if applicable)

Next Step

After v3 migration, use migrate-mstest-v3-to-v4 for MSTest v4.

Common Pitfalls