basic.yml

# This could be the simplest use case. It uses the latest stable version of Nim
steps:
  - uses: nim-lang/setup-nim@master
  - uses: actions/checkout@v2
  - run: nimble build

matrix.yml

jobs:
  test:
    strategy:
      matrix:
        os: ['windows-latest', 'macos-latest', 'ubuntu-latest']
        nim:
          - devel  # same meaning as choosenim devel
          - stable # same meaning as choosenim stable
          - 1.4    # latest nightly of 1.4 line
          - 1.2.4  # 1.2.4 release (not nightly)
          - 1.2.6
          - 0869d2a47777685d221ddde927f0175096c911b0 # build a specific commit

    name: Nim ${{ matrix.nim }} on ${{ matrix.os }}
    runs-on: ${{ matrix.os }}
    steps:
      - uses: actions/checkout@v2
      - uses: nim-lang/setup-nim@master
        with:
          version: ${{ matrix.nim }}
      - run: nimble test