run-tests

What this skill does

# Run .NET Tests

Detect the test platform and framework, run tests, and apply filters using `dotnet test`.

## When to Use

- User wants to run tests in a .NET project
- User needs to run a subset of tests using filters
- User needs help detecting which test platform (VSTest vs MTP) or framework is in use
- User wants to understand the correct filter syntax for their setup

## When Not to Use

- User needs to write or generate test code (use `writing-mstest-tests` for MSTest, or general coding assistance for other frameworks)
- User needs to migrate from VSTest to MTP (use `migrate-vstest-to-mtp`)
- User wants to iterate on failing tests without rebuilding (use `mtp-hot-reload`)
- User needs CI/CD pipeline configuration (use CI-specific skills)
- User needs to debug a test (use debugging skills)

## Inputs

| Input | Required | Description |
|-------|----------|-------------|
| Project or solution path | No | Path to the test project (.csproj) or solution (.sln). Defaults to current directory. |
| Filter expression | No | Filter expression to select specific tests |
| Target framework | No | Target framework moniker to run against (e.g., `net8.0`) |

## Critical Rules — Avoid Cross-Platform Mistakes

These are the most common agent mistakes. Internalize before proceeding:

| Rule | Why |
|------|-----|
| **Do NOT use `--logger trx`** for MTP projects | MTP uses `--report-trx` (requires the TrxReport extension package) |
| **Do NOT use `--report-trx`** for VSTest projects | VSTest uses `--logger trx` |
| **Do NOT use `-- --arg`** on .NET SDK 10+ | SDK 10+ passes MTP args directly: `dotnet test --project . --report-trx` |
| **Do NOT omit `--`** on .NET SDK 8/9 with MTP | SDK 8/9 requires the separator: `dotnet test -- --report-trx` |
| **Do NOT use `--filter "ClassName=..."`** with xUnit v3 on MTP | xUnit v3 on MTP uses `--filter-class`, `--filter-method`, `--filter-trait` |
| **Do NOT use bare positional path** on SDK 10+ | Use `--project <path>` or `--solution <path>` instead |
| **Do NOT use `--blame`** for MTP projects | MTP uses `--blame-crash` and `--blame-hang-timeout` separately (each requires its extension package) |
| **Do NOT use `--collect "Code Coverage"`** for MTP | MTP uses `--coverage` (requires the CodeCoverage extension package) |

## Workflow

### Quick Reference

| Platform | SDK | Command pattern |
|----------|-----|----------------|
| VSTest | Any | `dotnet test [<path>] [--filter <expr>] [--logger trx]` |
| MTP | 8 or 9 | `dotnet test [<path>] -- <MTP_ARGS>` |
| MTP | 10+ | `dotnet test --project <path> <MTP_ARGS>` |

**Detection files to always check** (in order): `global.json` -> `.csproj` -> `Directory.Build.props` -> `Directory.Packages.props`

**If the prompt names a subset of tests** (e.g., "integration tests", "smoke tests", a specific class, a specific TFM), plan to apply the matching filter / `--framework` in [Step 3](#step-3-run-filtered-tests) — do not run the whole suite.

### Step 1: Detect the test platform and framework

1. Run `dotnet --version` in the project directory to determine the SDK version. This accounts for `global.json` SDK pinning.
2. Read `global.json` — on .NET SDK 10+, `"test": { "runner": "Microsoft.Testing.Platform" }` is the **authoritative MTP signal**. If present, the project uses MTP and SDK 10+ syntax (no `--` separator).
3. Read `.csproj`, `Directory.Build.props`, **and** `Directory.Packages.props` for framework packages and MTP properties. **Always check all three files** — MTP properties are frequently set in `Directory.Build.props` rather than individual `.csproj` files.
4. For full detection logic (SDK 8/9 signals, framework identification), see the `platform-detection` skill.

**What to look for in each file:**

| File | Look for | Indicates |
|------|----------|-----------|
| `global.json` | `"test": { "runner": "Microsoft.Testing.Platform" }` | MTP on SDK 10+ |
| `global.json` | `"sdk": { "version": "..." }` | SDK version (determines `--` separator behavior) |
| `.csproj` | `<TestingPlatformDotnetTestSupport>true` | MTP on SDK 8/9 |
| `.csproj` | `MSTest`, `xunit.v3`, `NUnit`, `TUnit` packages | Framework identity |
| `.csproj` | `Microsoft.NET.Test.Sdk` + test adapter | VSTest (unless overridden by MTP signals above) |
| `.csproj` | `<TargetFrameworks>` (plural) | Multi-TFM — may need `--framework` |
| `Directory.Build.props` | `<TestingPlatformDotnetTestSupport>true` | MTP on SDK 8/9 (often set here, not in .csproj) |
| `Directory.Packages.props` | Centrally managed test package versions | Framework identity for CPM repos |

**Quick detection summary:**

| Signal | Means |
|--------|-------|
| `global.json` has `"test": { "runner": "Microsoft.Testing.Platform" }` | **MTP on SDK 10+** — pass args directly, no `--` |
| `<TestingPlatformDotnetTestSupport>true` in csproj or Directory.Build.props | **MTP on SDK 8/9** — pass args after `--` |
| Neither signal present | **VSTest** |

### Step 2: Run tests

#### VSTest (any .NET SDK version)

```bash
dotnet test [<PROJECT> | <SOLUTION> | <DIRECTORY> | <DLL> | <EXE>]
```

Common flags:

| Flag | Description |
|------|-------------|
| `--framework <TFM>` | Target a specific framework in multi-TFM projects (e.g., `net8.0`) |
| `--no-build` | Skip build, use previously built output |
| `--filter <EXPRESSION>` | Run selected tests (see [Step 3](#step-3-run-filtered-tests)) |
| `--logger trx` | Generate TRX results file |
| `--collect "Code Coverage"` | Collect code coverage using Microsoft Code Coverage (built-in, always available) |
| `--blame` | Enable blame mode to detect tests that crash the host |
| `--blame-crash` | Collect a crash dump when the test host crashes |
| `--blame-hang-timeout <duration>` | Abort test if it hangs longer than duration (e.g., `5min`) |
| `-v <level>` | Verbosity: `quiet`, `minimal`, `normal`, `detailed`, `diagnostic` |

#### MTP with .NET SDK 8 or 9

With `<TestingPlatformDotnetTestSupport>true</TestingPlatformDotnetTestSupport>`, `dotnet test` bridges to MTP but uses VSTest-style argument parsing. MTP-specific arguments must be passed after `--`:

```bash
dotnet test [<PROJECT> | <SOLUTION> | <DIRECTORY> | <DLL> | <EXE>] -- <MTP_ARGUMENTS>
```

#### MTP with .NET SDK 10+

With the `global.json` runner set to `Microsoft.Testing.Platform`, `dotnet test` natively understands MTP arguments without `--`:

```bash
dotnet test
    [--project <PROJECT_OR_DIRECTORY>]
    [--solution <SOLUTION_OR_DIRECTORY>]
    [--test-modules <EXPRESSION>]
    [<MTP_ARGUMENTS>]
```

Examples:

```bash
# Run all tests in a project
dotnet test --project path/to/MyTests.csproj

# Run all tests in a directory containing a project
dotnet test --project path/to/

# Run all tests in a solution (sln, slnf, slnx)
dotnet test --solution path/to/MySolution.sln

# Run all tests in a directory containing a solution
dotnet test --solution path/to/

# Run with MTP flags
dotnet test --project path/to/MyTests.csproj --report-trx --blame-hang-timeout 5min
```

> **Note**: The .NET 10+ `dotnet test` syntax does **not** accept a bare positional argument like the VSTest syntax. Use `--project`, `--solution`, or `--test-modules` to specify the target.

#### Common MTP flags

These flags apply to MTP on both SDK versions. On SDK 8/9, pass after `--`; on SDK 10+, pass directly.

> **Important:** `dotnet test`/MSBuild flags such as `--framework`, `--no-build`, `--configuration`, and `--verbosity` are consumed by `dotnet test` itself (they drive restore/build/host selection) and **always go BEFORE `--`**, regardless of platform or SDK. Only MTP test-platform arguments go after `--` on SDK 8/9. For example: `dotnet test --framework net9.0 -- --report-trx` (built-in flag before `--`, MTP extension flag after).

**Built-in flags (always available):**

| Flag | Description |
|------|-------------|
| `--results-directory <DIR>` | Directory for test result output |
| `--diagnostic` | Enable diagnostic logging for the test platform |
| `--diagnostic-output-director