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PARALLEL_TEST_EXECUTION.md

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Parallel Test Execution Configuration

This workspace is configured to run all three test projects in parallel in Visual Studio Test Explorer.

Configuration Files

.runsettings (Solution Root)

  • Enables parallel test execution at the assembly level
  • MaxCpuCount=0 uses all available processors to run test assemblies in parallel
  • DisableParallelization=false ensures parallelization is enabled

xunit.runner.json (In Each Test Project)

Each test project contains an xunit.runner.json file with:

  • parallelizeAssembly: true - Allows tests from this assembly to run in parallel with other assemblies
  • parallelizeTestCollections: true - Runs test collections within the assembly in parallel
  • maxParallelThreads: 0 - Uses xUnit's default algorithm (processors × 2)

How to Use in Visual Studio

Option 1: Configure via Test Explorer Settings

  1. Open Test Explorer (Test ? Test Explorer)
  2. Click the settings icon (??) in the toolbar
  3. Select Configure Run Settings ? Select Solution Wide runsettings File
  4. Browse to and select the .runsettings file at the solution root

Option 2: Configure via Visual Studio Settings

  1. Go to Tools ? Options
  2. Navigate to Test ? General
  3. Under Run Settings File, browse and select the .runsettings file

Option 3: Automatic Detection

Visual Studio will automatically detect and use .runsettings in the solution root in most cases.

Verification

After configuration, when you run all tests:

  • The three test projects (UnitTests, IntegrationTests, FunctionalTests) will run in parallel
  • Within each project, test collections will also run in parallel
  • You should see multiple tests running simultaneously in Test Explorer

Performance Considerations

Recommended for:

  • Fast unit tests (UnitTests project)
  • Independent integration tests that don't share state

Use with caution for:

  • Tests using shared resources (databases, files, ports)
  • Tests with Testcontainers - these may need collection fixtures to control parallelization

If you encounter issues with FunctionalTests (which use Testcontainers), you may need to:

  1. Disable parallelization for that specific project by setting parallelizeAssembly: false in its xunit.runner.json
  2. Use xUnit Collection Fixtures to control which tests can run in parallel
  3. Configure Testcontainers to use unique ports/databases per test class

Disabling Parallel Execution

To disable parallel execution for a specific test project, update its xunit.runner.json:

{
  "shadowCopy": false,
  "parallelizeAssembly": false,
  "parallelizeTestCollections": false
}

Command Line Usage

To use the .runsettings file when running tests from the command line:

dotnet test --settings .runsettings

Related Documentation