How to Run dotnet Tests in Parallel in CI

xUnit parallelizes test collections within an assembly, and you can shard assemblies across jobs with dotnet test filters.

Enable collection parallelism in xUnit config, then split coarse groups across CI jobs using dotnet test --filter by category or namespace.

xUnit config

{
  "parallelizeTestCollections": true,
  "maxParallelThreads": 0
}

Workflow

jobs:
  test:
    runs-on: ubuntu-latest
    strategy:
      fail-fast: false
      matrix:
        category: [Unit, Integration, Contract]
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-dotnet@v4
      - run: dotnet test --filter "Category=${{ matrix.category }}"

Gotchas

• maxParallelThreads: 0 uses the machine core count; set a number to cap it.
• Tests in the same collection do not run in parallel with each other by design.

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