these 2 derivations will be built:
  /nix/store/81kzd9lzisf9q529xpkv7gpz8x3plymq-test-drv-canary-actual.drv
  /nix/store/rvfpwvq5fprx891pc716kfn4g2yixq1c-test-drv-canary.drv