# xUnit -> MSTest Mapping Cheatsheet

Comprehensive reference loaded by the `migrate-xunit-to-mstest` skill. Look up specific xUnit constructs and their MSTest v4 equivalents, including edge cases and "no equivalent -- manual" calls.

Target framework throughout: **MSTest v4** (the few v3-only spellings are explicitly marked).

## Table of contents

- [1. Test discovery (class + method attributes)](#1-test-discovery-class--method-attributes)
- [2. Data-driven tests](#2-data-driven-tests)
- [3. Assertions](#3-assertions)
  - [3.1 Equality, null, reference](#31-equality-null-reference)
  - [3.2 Boolean](#32-boolean)
  - [3.3 Type checks](#33-type-checks)
  - [3.4 Numeric / comparison](#34-numeric--comparison)
  - [3.5 String](#35-string)
  - [3.6 Collection](#36-collection)
  - [3.7 Exceptions](#37-exceptions)
  - [3.8 Async exception assertions](#38-async-exception-assertions)
  - [3.9 Skip / inconclusive](#39-skip--inconclusive)
  - [3.10 Fail](#310-fail)
  - [3.11 No-equivalent assertions](#311-no-equivalent-assertions)
- [4. Fixtures and lifecycle](#4-fixtures-and-lifecycle)
- [5. Output / TestContext](#5-output--testcontext)
- [6. Cancellation and timeouts (xUnit v3 specifics)](#6-cancellation-and-timeouts-xunit-v3-specifics)
- [7. Parallelization](#7-parallelization)
- [8. Assembly-level attributes](#8-assembly-level-attributes)
- [9. Packages](#9-packages)
- [10. Companion / extension libraries](#10-companion--extension-libraries)

## 1. Test discovery (class + method attributes)

| xUnit | MSTest |
|---|---|
| *(no class attribute)* | `[TestClass]` (required) |
| *(no class modifier)* | Preserve the original hierarchy. Do **not** add `sealed` mechanically -- base/derived test classes are common in xUnit and sealing would break them. `writing-mstest-tests` can apply `sealed` as a follow-up where appropriate. |
| `[Fact]` | `[TestMethod]` |
| `[Theory]` | `[TestMethod]` (MSTest 3+ unified; `[DataTestMethod]` still works but is not needed) |
| `[Fact(DisplayName = "x")]` | MSTest 4: `[TestMethod(DisplayName = "x")]`; MSTest 3: `[TestMethod("x")]` |
| `[Theory(DisplayName = "x")]` | Same as above on the `[TestMethod]` |
| `[Fact(Skip = "reason")]` | `[TestMethod]` + `[Ignore("reason")]` (the `[Ignore]` attribute alone does not discover a test -- you still need `[TestMethod]`) |
| `[Fact(Timeout = 5000)]` | `[TestMethod]` + `[Timeout(5000)]` (same -- `[Timeout]` is a modifier, not a discovery attribute) |
| `[Trait("Category", "Unit")]` | `[TestCategory("Unit")]` |
| `[Trait("Owner", "alice")]` | `[Owner("alice")]` on each affected test method (`Owner` targets methods only; expand xUnit v3 class/assembly owner traits to their tests). `Owner` is a reserved VSTest property and is rejected by `TestPropertyAttribute` |
| `[Collection("Db")]` | Step 8 + Step 11: `[DoNotParallelize]` (serialization) + `[ClassInitialize]` (sharing) -- preserve scope explicitly |
| Custom `FactAttribute` subclass | Custom `TestMethodAttribute` subclass overriding `ExecuteAsync` (MSTest v4). See `writing-mstest-tests` and `migrate-mstest-v3-to-v4` for `CallerInfo` constructor pattern |
| Custom `TheoryAttribute` subclass | Same -- subclass `TestMethodAttribute`; expose data via `ITestDataSource` |

> Both `[TestCategory]` and `[TestProperty]` are **filterable** at runtime:
> - `[TestCategory("Unit")]` -> `--filter "TestCategory=Unit"` (VSTest) / `--filter-trait "TestCategory=Unit"` (MTP); targets `Assembly`, `Class`, and `Method`
> - `[Owner("alice")]` -> `--filter "Owner=alice"` (VSTest) / `--filter-trait "Owner=alice"` (MTP); targets `Method` only
> - `[TestProperty("Key", "Value")]` -> `--filter "Key=Value"` (VSTest) / `--filter-trait "Key=Value"` (MTP); targets `Class` and `Method` only (no `AttributeTargets.Assembly`)
>
> Use `[TestCategory]` for the conventional category trait, method-level `[Owner]` for the reserved owner property, and `[TestProperty]` for other key/value metadata at class/method scope. An `[assembly: Trait("Category", ...)]` in xUnit can be migrated to `[assembly: TestCategory(...)]`. Expand class/assembly owner traits to method-level `[Owner]` on every affected test, preserving each value. An assembly-level `[Trait]` with another arbitrary key cannot map to `[assembly: TestProperty(...)]` -- collapse it to `[assembly: TestCategory(...)]` only if that preserves filtering semantics, or move it down to every class (see Section 8).
>
> **Conditional skips** (xUnit `[Trait("OS", "Windows")]` patterns that gate execution): MSTest 3.10+ offers dedicated condition attributes -- `[OSCondition]` and `[CICondition]` -- which are usually a better fit than overloading `[TestCategory]` for environmental gating. (There is no `ArchitectureCondition` or `NonParallelizableCondition` attribute in MSTest; for non-parallel intent use `[DoNotParallelize]`, and for architecture gating fall back to `if (RuntimeInformation.OSArchitecture != ...) Assert.Inconclusive(...)`.) See Section 3.9.

## 2. Data-driven tests

| xUnit | MSTest |
|---|---|
| `[InlineData(1, 2)]` | `[DataRow(1, 2)]` |
| `[InlineData(1, DisplayName = "case 1")]` | `[DataRow(1, DisplayName = "case 1")]` |
| `[InlineData(null)]` | `[DataRow(null)]` |
| `[MemberData(nameof(Cases))]` returning `IEnumerable<object[]>` | `[DynamicData(nameof(Cases))]` returning `IEnumerable<object[]>` |
| `[MemberData(nameof(Cases), MemberType = typeof(X))]` | `[DynamicData(nameof(Cases), typeof(X))]` |
| `[MemberData(nameof(Cases))]` returning `TheoryData<int, string>` | `[DynamicData(nameof(Cases))]` returning `IEnumerable<object[]>`, `IEnumerable<(int, string)>` (MSTest 3.7+ ValueTuple), or `IEnumerable<TestDataRow<(int, string)>>` (strongly-typed with per-row `DisplayName`/`Ignore` metadata -- see [docs](https://learn.microsoft.com/en-us/dotnet/core/testing/unit-testing-mstest-writing-tests-data-driven#supported-data-source-types)) |
| `[MemberData(nameof(Method), arg1, arg2)]` (parameterized member) | **Manual** -- convert to a parameterless property/method, or move parameter logic into the test method |
| `[ClassData(typeof(MyData))]` where `MyData : IEnumerable<object[]>` | Expose a static `IEnumerable<object[]> Cases => new MyData();` and use `[DynamicData(nameof(Cases))]` |
| `[ClassData(typeof(MyData))]` where `MyData : TheoryData<...>` | Same approach; convert `TheoryData<...>` to `IEnumerable<object[]>` or ValueTuples |
| Custom `DataAttribute` subclass | **Manual** -- implement `ITestDataSource` (`GetData` + `GetDisplayName`) |

**Literal-type trap.** MSTest's `[DataRow]` enforces exact type matching against method parameters. xUnit's `[InlineData]` is more permissive. After conversion, audit literals:

| Parameter type | Required literal |
|---|---|
| `int` | `1`, `0`, `-1` |
| `long` | `1L` |
| `float` | `1.0f` |
| `double` | `1.0` or `1.0d` |
| `decimal` | `1.0m` |
| `uint` | `1U` |
| `Type` | `typeof(...)` |

## 3. Assertions

### 3.1 Equality, null, reference

| xUnit | MSTest |
|---|---|
| `Assert.Equal(expected, actual)` | `Assert.AreEqual(expected, actual)` |
| `Assert.Equal(expected, actual, comparer)` | `Assert.AreEqual(expected, actual, comparer)` |
| `Assert.Equal(0.1, 0.10001, 3)` (precision) | `Assert.AreEqual(0.1, 0.10001, delta: 0.001)` |
| `Assert.Equal("a", "A", ignoreCase: true)` | `Assert.AreEqual("a", "A", ignoreCase: true)` |
| `Assert.NotEqual(a, b)` | `Assert.AreNotEqual(a, b)` |
| `Assert.Same(a, b)` | `Assert.AreSame(a, b)` |
| `Assert.NotSame(a, b)` | `Assert.AreNotSame(a, b)` |
| `Assert.Null(x)` | `Assert.IsNull(x)` |
| `Assert.NotNull(x)` | `Assert.IsNotNull(x)` |
| `Assert.Equivalent(expected, actual)` | **Manual** -- no built-in deep-equality assertion. Use a third-party library (FluentAssertions `.Should().BeEquivalentTo(...)`) or write member-by-member assertions |

### 3.2 Boolean

| xUnit | MSTest |
|---|---|
| `Assert.True(x)` | `Assert.IsTrue(x)` |
| `Assert.False(x)` | `Assert.IsFalse(x)` |
| `Assert.True(x, "msg")` | `Assert.IsTrue(x, "msg")` |

### 3.3 Type checks

| xUnit | MSTest |
|---|---|
| `Assert.IsType<T>(x)` (exact type, returns `T`) | `var t = Assert.IsExactInstanceOfType<T>(x);` (MSTest 4.1+; returns the typed value, exact match) |
| `Assert.IsNotType<T>(x)` (exact type) | `Assert.IsNotExactInstanceOfType<T>(x);` (MSTest 4.1+) |
| `Assert.IsAssignableFrom<T>(x)` | `Assert.IsInstanceOfType<T>(x)` -- semantically equivalent (assignable-from check) |

> MSTest 4.1+ adds `Assert.IsExactInstanceOfType<T>(x)` -- the proper equivalent of xUnit's exact-type `Assert.IsType<T>` (returns `T`, single call). On pre-4.1 MSTest, fall back to `var t = Assert.IsInstanceOfType<T>(x); Assert.AreEqual(typeof(T), x.GetType());`. `Assert.IsInstanceOfType<T>(x)` on its own is **assignable-only** (= xUnit `Assert.IsAssignableFrom<T>`); silently mapping `IsType<T>` to it loses exact-type semantics.
>
> MSTest v4's `Assert.IsInstanceOfType<T>(x)` returns the typed value (no out param). MSTest v3 uses `Assert.IsInstanceOfType<T>(x, out var typed)`.

### 3.4 Numeric / comparison

| xUnit | MSTest |
|---|---|
| `Assert.InRange(value, low, high)` | `Assert.IsInRange(value, low, high)` |
| `Assert.NotInRange(value, low, high)` | `Assert.IsNotInRange(value, low, high)` |
| *(no direct API)* | `Assert.IsGreaterThan(low, value)` |
| *(no direct API)* | `Assert.IsLessThan(high, value)` |

### 3.5 String

| xUnit | MSTest |
|---|---|
| `Assert.Contains("sub", str)` | `Assert.Contains("sub", str)` (MSTest 3.8+); fallback `StringAssert.Contains(str, "sub")` |
| `Assert.DoesNotContain("sub", str)` | `Assert.DoesNotContain("sub", str)` (MSTest 3.8+); fallback `StringAssert.DoesNotMatch(...)` |
| `Assert.StartsWith("p", str)` | `Assert.StartsWith("p", str)` (MSTest 3.8+); fallback `StringAssert.StartsWith(str, "p")` |
| `Assert.EndsWith("s", str)` | `Assert.EndsWith("s", str)` (MSTest 3.8+); fallback `StringAssert.EndsWith(str, "s")` |
| `Assert.Matches("\\d+", str)` | `Assert.MatchesRegex(@"\d+", str)` |
| `Assert.DoesNotMatch("\\d+", str)` | `Assert.DoesNotMatchRegex(@"\d+", str)` |
| `Assert.Equal("a", "A", ignoreCase: true)` | `Assert.AreEqual("a", "A", ignoreCase: true)` |

### 3.6 Collection

| xUnit | MSTest |
|---|---|
| `Assert.Contains(item, collection)` | `Assert.Contains(item, collection)` |
| `Assert.DoesNotContain(item, collection)` | `Assert.DoesNotContain(item, collection)` |
| `Assert.Contains(collection, x => predicate)` | `Assert.IsTrue(collection.Any(x => predicate))` |
| `Assert.Empty(collection)` | `Assert.IsEmpty(collection)` |
| `Assert.NotEmpty(collection)` | `Assert.IsNotEmpty(collection)` |
| `Assert.Single(collection)` | `var item = Assert.ContainsSingle(collection);` (returns the element) |
| `Assert.Single(collection, predicate)` | `var item = Assert.ContainsSingle(collection.Where(predicate));` |
| `Assert.Collection(items, e1 => ..., e2 => ...)` | **Manual** -- assert count, then per-element. No idiomatic MSTest equivalent |
| `Assert.All(items, x => assertion(x))` | **Manual** -- `foreach (var x in items) assertion(x);` |
| `Assert.Equal(expected, actual)` on `IEnumerable<T>` (element-wise) | `Assert.AreSequenceEqual(expected, actual)` (MSTest 4.3+); pre-4.3: `CollectionAssert.AreEqual(expected.ToList(), actual.ToList())` (`IList` required). Plain `Assert.AreEqual` does **not** compare element-wise (MSTEST0065). |
| `Assert.Equal(expected, actual, comparer)` on collections | `Assert.AreSequenceEqual(expected, actual, comparer)` (MSTest 4.3+); pre-4.3: `CollectionAssert.AreEqual(expected.ToList(), actual.ToList(), comparer)` |
| `Assert.Distinct(collection)` | **Manual** -- `Assert.AreEqual(collection.Count, collection.Distinct().Count())` |
| `Assert.Superset(expected, actual)` | **Manual** -- `Assert.IsTrue(expected.IsSubsetOf(actual))` if both are `HashSet<T>` |

### 3.7 Exceptions

> **Semantic trap**: xUnit `Assert.Throws<T>` = **exact type**. xUnit `Assert.ThrowsAny<T>` = **derived types also match**. The names invert between the frameworks.

| xUnit | MSTest |
|---|---|
| `Assert.Throws<T>(() => ...)` | **`Assert.ThrowsExactly<T>(() => ...)`** |
| `Assert.ThrowsAny<T>(() => ...)` | **`Assert.Throws<T>(() => ...)`** |
| `Assert.Throws<T>(paramName, () => ...)` (ArgumentException family) | `var ex = Assert.ThrowsExactly<T>(() => ...); Assert.AreEqual(paramName, ex.ParamName);` |
| `Record.Exception(() => ...)` | **Manual** -- `try { ...; return null; } catch (Exception ex) { return ex; }`. If you only need to assert a specific type, use `Assert.ThrowsExactly<T>` directly |

### 3.8 Async exception assertions

| xUnit | MSTest |
|---|---|
| `await Assert.ThrowsAsync<T>(() => task)` | `await Assert.ThrowsExactlyAsync<T>(() => task)` |
| `await Assert.ThrowsAnyAsync<T>(() => task)` | `await Assert.ThrowsAsync<T>(() => task)` |
| `await Record.ExceptionAsync(() => task)` | **Manual** -- `try { await task; return null; } catch (Exception ex) { return ex; }` |

### 3.9 Skip / inconclusive

> xUnit `Assert.Skip*` is **runtime** (decided inside the test body). MSTest `[Ignore]` is **compile-time** (decided at discovery). They are not interchangeable -- mapping `SkipUnless` to `[Ignore]` will permanently exclude the test on machines where it should have run.
>
> **Prefer MSTest's condition attributes** (`[OSCondition]` and `[CICondition]` -- MSTest 3.10+) over `Assert.Inconclusive` when the condition is OS- or CI-environmental. They are discoverable, reportable per-condition, and do not pollute the test body with skip plumbing. (MSTest does **not** ship an `ArchitectureCondition` or `NonParallelizableCondition` attribute -- for architecture gating fall back to runtime `Assert.Inconclusive`; for "do not run in parallel" use `[DoNotParallelize]`.)

| xUnit | MSTest |
|---|---|
| `[Fact(Skip = "reason")]` | `[TestMethod]` + `[Ignore("reason")]` |
| `Assert.Skip("reason")` (xUnit v3) | `Assert.Inconclusive("reason")` |
| `Assert.SkipWhen(condition, "reason")` (xUnit v3) | If `condition` is environmental: `[OSCondition(...)]` / `[CICondition(...)]` / etc. Otherwise: `if (condition) Assert.Inconclusive("reason");` |
| `Assert.SkipUnless(condition, "reason")` (xUnit v3) | Same -- prefer a condition attribute when the predicate is environmental; otherwise `if (!condition) Assert.Inconclusive("reason");` |
| `Assert.SkipUnless(OperatingSystem.IsWindows(), "...")` | `[OSCondition(OperatingSystems.Windows)]` on the method |
| `Assert.SkipWhen(Environment.GetEnvironmentVariable("CI") != null, "...")` | `[CICondition(ConditionMode.Exclude)]` on the method |

### 3.10 Fail

| xUnit | MSTest |
|---|---|
| `Assert.Fail("reason")` | `Assert.Fail("reason")` |

### 3.11 No-equivalent assertions

These xUnit assertions have no MSTest equivalent. Convert each manually:

| xUnit | Manual replacement |
|---|---|
| `Assert.Collection(items, e1Inspector, e2Inspector, ...)` | `Assert.HasCount(N, items); var arr = items.ToArray(); e1Inspector(arr[0]); ...` |
| `Assert.All(items, inspector)` | `foreach (var item in items) inspector(item);` |
| `Assert.Equivalent(expected, actual)` | Deep-compare manually, or use FluentAssertions / Verify |
| `Assert.Raises<T>(addHandler, removeHandler, () => trigger())` | Manual subscribe/flag/unsubscribe |
| `Assert.RaisesAny<T>(...)` | Same -- manual handler |
| `Assert.PropertyChanged(notifier, "Prop", () => action)` | Subscribe to `INotifyPropertyChanged.PropertyChanged`, set a flag, assert |
| `Assert.PropertyChangedAsync(notifier, "Prop", async () => action)` | Same, with `await` |

## 4. Fixtures and lifecycle

### Test-class lifecycle (per-test)

| xUnit | MSTest |
|---|---|
| Constructor (sync setup) | Keep the constructor (MSTest also instantiates one instance per test method) |
| Constructor taking `ITestOutputHelper output` | Constructor taking `TestContext testContext` (MSTest 3.6+) |
| `Dispose()` | Keep `Dispose()` (MSTest supports `IDisposable`) **or** convert to `[TestCleanup] public void Cleanup()` |
| `IAsyncDisposable.DisposeAsync()` | Keep `DisposeAsync()` (MSTest supports `IAsyncDisposable`) **or** `[TestCleanup] public async Task CleanupAsync()` |
| `IAsyncLifetime.InitializeAsync()` | `[TestInitialize] public async Task InitAsync()` |
| `IAsyncLifetime.DisposeAsync()` | `[TestCleanup] public async Task CleanupAsync()` |

> Per `writing-mstest-tests`: prefer the constructor for sync initialization (it allows `readonly` fields and works correctly with nullability). Use `[TestInitialize]` only for async setup or when `TestContext` is needed but you have not adopted constructor injection.

### Class-level fixtures (shared across tests in one class)

xUnit `IClassFixture<T>` -- one fixture instance per test class, shared by every test method in that class:

```csharp
// xUnit
public class DbFixture : IDisposable { /* ... */ }

public class OrderTests : IClassFixture<DbFixture>
{
    private readonly DbFixture _fixture;
    public OrderTests(DbFixture fixture) => _fixture = fixture;
}
```

```csharp
// MSTest equivalent
[TestClass]
public sealed class OrderTests
{
    private static DbFixture? s_fixture;

    [ClassInitialize]
    public static void ClassInit(TestContext context) => s_fixture = new DbFixture();

    [ClassCleanup]
    public static void ClassCleanup() => s_fixture?.Dispose();
}
```

### Cross-class fixtures (`ICollectionFixture<T>` / `[CollectionDefinition]`)

xUnit collections do two things at once: (1) share a fixture instance across multiple test classes, **and** (2) serialize execution of those classes (no parallel execution within a collection). MSTest decouples these:

- **Sharing** -> `[AssemblyInitialize]` (genuinely process-wide) **or** static `Lazy<T>` shared helper referenced by each class's `[ClassInitialize]`
- **Serialization** -> `[DoNotParallelize]` on each member class

Map deliberately:

| xUnit collection setup | MSTest equivalent |
|---|---|
| `[CollectionDefinition("Db")]` + `ICollectionFixture<DbFixture>`, member classes have `[Collection("Db")]`, parallelization default | Static `Lazy<DbFixture>` helper + `[ClassInitialize]` per class. No `[DoNotParallelize]` needed |
| Same but `[CollectionDefinition("Db", DisableParallelization = true)]` | Same as above + `[DoNotParallelize]` on each member class |
| Genuinely process-wide singleton (e.g., `WebApplicationFactory` for a TestServer the whole assembly hits) | `[AssemblyInitialize]` + `[AssemblyCleanup]` in a dedicated `AssemblySetup` class -- with the user's explicit acknowledgement that scope widens to the whole assembly |
| Custom `ITestCollectionOrderer` | **Manual** -- MSTest's `[TestMethodAttribute]` ordering model is different; flag for review |

### Assembly-level fixtures

| xUnit | MSTest |
|---|---|
| *(no built-in -- emulated via assembly-scoped `[CollectionDefinition]` + `ICollectionFixture<T>`)* | `[AssemblyInitialize] public static void AssemblyInit(TestContext context)` and `[AssemblyCleanup] public static void AssemblyCleanup()` -- in any class marked `[TestClass]` |

## 5. Output / TestContext

| xUnit | MSTest |
|---|---|
| `ITestOutputHelper` constructor parameter | `TestContext` constructor parameter (MSTest 3.6+) or `public TestContext TestContext { get; set; } = null!;` property |
| `_output.WriteLine("...")` | `_testContext.WriteLine("...")` |
| `_output.WriteLine("fmt {0}", arg)` (xUnit v2) | `_testContext.WriteLine($"fmt {arg}")` (interpolation -- MSTest v4 dropped most format-string overloads) |
| `TestContext.Current.TestOutputHelper.WriteLine(...)` (xUnit v3) | `_testContext.WriteLine(...)` |
| `TestContext.Current.AddAttachment(name, contents)` (xUnit v3) | `_testContext.AddResultFile(pathOnDisk)` |
| `TestContext.Current.TestMethod.MethodInfo.Name` (xUnit v3) | `_testContext.TestName` |
| `TestContext.Current.TestClass.Class.Name` (xUnit v3) | `_testContext.FullyQualifiedTestClassName` |

## 6. Cancellation and timeouts (xUnit v3 specifics)

| xUnit v3 | MSTest |
|---|---|
| `TestContext.Current.CancellationToken` | `_testContext.CancellationToken` (MSTest 3.6+; instance `TestContext` from constructor or property injection -- **never** replace with a new `CancellationTokenSource`, that breaks linkage to test-host cancellation) |
| `[Fact(Timeout = 5000)]` | `[Timeout(5000)]` |
| `[Fact(Timeout = -1)]` (no timeout) | Omit `[Timeout]` (MSTest default = no timeout) |

xUnit v2 has no equivalent of `TestContext.Current.CancellationToken` -- skip this row for v2 sources.

## 7. Parallelization

| xUnit default | MSTest equivalent |
|---|---|
| Parallel across test classes, serial within a class | `[assembly: Parallelize(Workers = 0, Scope = ExecutionScope.ClassLevel)]` |
| xUnit + `[CollectionBehavior(DisableTestParallelization = true)]` | Omit `[assembly: Parallelize]` |
| xUnit + `[CollectionBehavior(MaxParallelThreads = N)]` | `[assembly: Parallelize(Workers = N, Scope = ExecutionScope.ClassLevel)]` |
| `[Collection("Db")]` (forces serial within the collection) | `[DoNotParallelize]` on each member class |
| `[CollectionDefinition("Db", DisableParallelization = true)]` | Same -- `[DoNotParallelize]` on each member class |

> Do not use `ExecutionScope.MethodLevel` to "match xUnit". MethodLevel parallelizes methods *within* a class, which xUnit never does.

### `xunit.runner.json`

Delete `xunit.runner.json` after porting the settings that affect behavior:

| xUnit setting | MSTest equivalent |
|---|---|
| `"parallelizeAssembly": false` | MSTest's serial default; omit `[assembly: Parallelize]` |
| `"parallelizeTestCollections": false` | MSTest's serial default; omit `[assembly: Parallelize]` |
| `"maxParallelThreads": N` | `[assembly: Parallelize(Workers = N, Scope = ExecutionScope.ClassLevel)]` |
| `"diagnosticMessages": true` | Use diagnostic CLI output or `.runsettings` verbosity |
| `"longRunningTestSeconds": N` | `[Timeout(N * 1000)]` on affected tests |
| `"methodDisplay"` / `"preEnumerateTheories"` / `"appDomain"` | No direct equivalent; document the behavior change |

## 8. Assembly-level attributes

xUnit assembly attributes split into two groups: a few have direct MSTest equivalents (and stay at assembly scope); the rest must be removed or reimplemented against MSTest extensibility.

| xUnit | Disposition |
|---|---|
| `[assembly: CollectionBehavior(...)]` | Remove -- replaced by `[assembly: Parallelize(...)]` (Section 7) |
| `[assembly: TestCaseOrderer(...)]` | Remove + reimplement with MSTest extensibility if needed (flag for manual) |
| `[assembly: TestCollectionOrderer(...)]` | Remove + flag for manual |
| `[assembly: TestFramework(...)]` | Remove |
| `[assembly: CaptureConsole]` (xUnit v3) | Remove -- MSTest does not capture console by default |
| `[assembly: Xunit.Trait("Category", "v")]` | `[assembly: TestCategory("v")]` (applies the category to every test in the assembly -- `TestCategoryAttribute` targets `Assembly`, `Class`, and `Method`) |
| `[assembly: Xunit.Trait("Owner", "alice")]` | `[Owner("alice")]` on every affected test method; never at assembly or class scope |
| `[assembly: Xunit.Trait("k", "v")]` (other non-category/non-owner key) | **No direct equivalent at assembly scope** -- `TestPropertyAttribute` targets only `Class`/`Method`. Either collapse to `[assembly: TestCategory("v")]` if the value alone filters cleanly, or push down to every test class as `[TestProperty("k", "v")]` |

For owner traits, calculate each test's effective metadata before removing the
xUnit attributes. Deduplicate identical owner values. If method, class, or
assembly owners conflict, or an inherited/shared test method cannot preserve
different effective owners across its classes, flag the mapping for manual
review rather than silently choosing or overwriting an owner. Never route
`Owner` through the generic `TestProperty` or category fallback.

## 9. Packages

**Remove** every xUnit package from `.csproj`, `Directory.Build.props`, `Directory.Packages.props`:

- `xunit`, `xunit.abstractions`, `xunit.assert`, `xunit.core`
- `xunit.extensibility.core`, `xunit.extensibility.execution`
- `xunit.runner.visualstudio`
- `xunit.v3`, `xunit.v3.assert`, `xunit.v3.core`, `xunit.v3.extensibility.core`
- `xunit.v3.mtp-v1`, `xunit.v3.mtp-v2`, `xunit.v3.core.mtp-v1`, `xunit.v3.core.mtp-v2`
- `YTest.MTP.XUnit2` (xUnit v2 MTP shim)

**Add** MSTest v4 -- pick exactly one of:

The versions below are illustrative known-compatible pins. Resolve the current stable versions
from the project's configured package source and pin those exact versions during a real migration.

```xml
<!-- Option A: metapackage (includes Microsoft.NET.Test.Sdk + TestAdapter + TestFramework + Analyzers) -->
<PackageReference Include="MSTest" Version="4.1.0" />
<!-- Keep VSTest explicit and reviewable when that is the source runner. -->
<PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.0.1" />
```

The explicit `Microsoft.NET.Test.Sdk` line intentionally duplicates the metapackage's transitive
dependency: when preserving VSTest, retain and update a source project's explicit pin so runner and
version compatibility remain reviewable. For the illustrated MSTest 4.1.0 pin, use 18.0.1+;
keeping 17.x causes `NU1605`. Do not add an explicit pin to an MTP project that did not have one.

```xml
<!-- Option B: MSTest.Sdk -- 4.1.0 is an example resolved pin; it defaults to MTP. -->
<!-- Set <UseVSTest>true</UseVSTest> to preserve VSTest. UseVSTest supplies
     Microsoft.NET.Test.Sdk, but retain a source project's existing explicit pin. -->
<Project Sdk="MSTest.Sdk/4.1.0">
  <PropertyGroup>
    <!-- Keep the project's existing TargetFramework; do not change it during migration. -->
    <UseVSTest>true</UseVSTest> <!-- omit this line to stay on MTP -->
  </PropertyGroup>
</Project>
```

Prefer pinning the resolved exact `MSTest.Sdk` version in `global.json` (especially in solutions with several test projects) so the version lives in one place. The `4.1.0` below remains the same illustrative pin:

```json
{
  "msbuild-sdks": {
    "MSTest.Sdk": "4.1.0"
  }
}
```

With the pin in `global.json`, the project line simplifies to `<Project Sdk="MSTest.Sdk">`.

`MSTest.Sdk` adds `Microsoft.VisualStudio.TestTools.UnitTesting` as an **implicit global using**, so:

- **Do not** add `<Using Include="Microsoft.VisualStudio.TestTools.UnitTesting" />` to the project file -- it's redundant noise.
- **Do not** add `using Microsoft.VisualStudio.TestTools.UnitTesting;` to each test file -- it's already in scope.

(Option A -- the `MSTest` metapackage -- does not bring the global using; per-file `using Microsoft.VisualStudio.TestTools.UnitTesting;` is still required there.)

## 10. Companion / extension libraries

| xUnit companion | MSTest equivalent |
|---|---|
| `Xunit.SkippableFact` (`[SkippableFact]`, `Skip.If`, `Skip.IfNot`) | `[Ignore]` (compile-time) or `Assert.Inconclusive("reason")` (runtime). Remove the package |
| `Xunit.Combinatorial` (`[CombinatorialData]`, `[CombinatorialValues]`) | [`Combinatorial.MSTest`](https://github.com/Youssef1313/Combinatorial.MSTest) (community port) -- attribute surface is the same as xUnit.Combinatorial. Alternatively, expand combinations into explicit `[DataRow]`s or compute them in `[DynamicData]` |
| `Xunit.StaFact` (`[StaFact]`, `[WpfFact]`) | No equivalent -- manual STA thread or flag for review |
| `Xunit.Priority` (`[TestCaseOrderer]`) | MSTest ordering is different -- flag for manual |
| `Verify.Xunit` | `Verify.MSTest` (swap the package; same usage) |
| `FluentAssertions` / `Shouldly` / `AwesomeAssertions` | Keep the existing package and namespace -- assertion libraries are framework-agnostic. `AwesomeAssertions` uses the `AwesomeAssertions` namespace, not `FluentAssertions`. Only if the user explicitly requests a package swap, update matching `using`, `global using`, and project `<Using Include="...">` imports along with the package reference. |
| `Moq` / `NSubstitute` / `FakeItEasy` | Keep -- mocking libraries are framework-agnostic |
| `AutoFixture.Xunit2` (`[AutoData]`) | `AutoFixture` core works, but the auto-data attribute integration requires the xUnit-specific package -- flag for manual |