Thanks I thought that the os should be defined as matrix but this not case
S name: PharoVersion env: GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }} on: push: branches: - master jobs: build: runs-on: [ ubuntu-latest, mac-latest ] strategy: matrix: smalltalk: [ Pharo64-8.0, Pharo64-9.0 ] name: ${{ matrix.smalltalk }} steps: - uses: actions/checkout@v2 - uses: hpi-swa/setup-smalltalkCI@v1 with: smalltalk-version: ${{ matrix.smalltalk }} - name: Load Image and Run Tests run: smalltalkci -s ${{ matrix.smalltalk }} env: GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }} timeout-minutes: 15