We can use continuous integration (CI) services such as GitHub Action and Travis CI to automatically validate future backends via the future.tests test suite.

Here is an example of a .github/workflow/future.tests.yaml file that configures GitHub Actions to check several backends via the future.tests test suite.

on: [push, pull_request]

name: future_tests

jobs:
  future_tests:
    if: "! contains(github.event.head_commit.message, '[ci skip]')"    

    runs-on: ubuntu-20.04

    name: future.plan=${{ matrix.future.plan }}

    strategy:
      fail-fast: false
      matrix:
        future:
          - { plan: 'cluster'                             }
          - { plan: 'multicore'                           }
          - { plan: 'multisession'                        }
          - { plan: 'sequential'                          }
          - { plan: 'future.batchtools::batchtools_local' }
          - { plan: 'future.callr::callr'                 }

    env:
      GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}
      RSPM: https://packagemanager.rstudio.com/cran/__linux__/focal/latest
      R_REMOTES_NO_ERRORS_FROM_WARNINGS: true
      ## R CMD check
      _R_CHECK_LENGTH_1_CONDITION_: true
      _R_CHECK_LENGTH_1_LOGIC2_: true
      _R_CHECK_MATRIX_DATA_: true
      _R_CHECK_CRAN_INCOMING_: false
      ## Specific to futures
      R_FUTURE_RNG_ONMISUSE: error
      
    steps:
      - uses: actions/checkout@v2

      - uses: r-lib/actions/setup-r@master
        with:
          r-version: release

      - uses: r-lib/actions/setup-pandoc@master

      - name: Query R package dependencies
        run: |
          install.packages('remotes')
          saveRDS(remotes::dev_package_deps(dependencies = TRUE), ".github/depends.Rds", version = 2)
          writeLines(sprintf("R-%i.%i", getRversion()$major, getRversion()$minor), ".github/R-version")
        shell: Rscript {0}

      - name: Cache R packages
        uses: actions/cache@v1
        with:
          path: ${{ env.R_LIBS_USER }}
          key: ${{ runner.os }}-${{ hashFiles('.github/R-version') }}-1-${{ hashFiles('.github/depends.Rds') }}
          restore-keys: ${{ runner.os }}-${{ hashFiles('.github/R-version') }}-1-

      - name: Install R package system dependencies (Linux)
        if: runner.os == 'Linux'
        env:
          RHUB_PLATFORM: linux-x86_64-ubuntu-gcc
        run: |
          Rscript -e "remotes::install_github('r-hub/sysreqs')"
          sysreqs=$(Rscript -e "cat(sysreqs::sysreq_commands('DESCRIPTION'))")
          sudo -s eval "$sysreqs"

      - name: Install R package dependencies
        run: |
          remotes::install_deps(dependencies = TRUE)
          install.packages(".", repos=NULL, type="source")  ## needed by parallel workers
        shell: Rscript {0}
          
      - name: Install 'future.tests' and any backend R packages
        run: |
          remotes::install_cran("future.tests")
          if (grepl("::", plan <- "${{ matrix.future.plan }}") && nzchar(pkg <- sub("::.*", "", plan))) install.packages(pkg)
        shell: Rscript {0}

      - name: Session info
        run: |
          options(width = 100)
          pkgs <- installed.packages()[, "Package"]
          sessioninfo::session_info(pkgs, include_base = TRUE)
        shell: Rscript {0}
    
      - name: Check future backend '${{ matrix.future.plan }}'
        run: |
          R CMD build --no-build-vignettes --no-manual . 
          R CMD INSTALL *.tar.gz 
          Rscript -e future.tests::check --args --test-plan=${{ matrix.future.plan }}

      - name: Upload check results
        if: failure()
        uses: actions/upload-artifact@master
        with:
          name: ${{ runner.os }}-r${{ matrix.future.plan }}-results
          path: check

For real-world examples, see the GitHub repositories of future, future.batchtools, and future.callr.