The test itself can be run interactively. This is particularly useful when developing or debugging a test: $ nix-build nixos/tests/login.nix -A driver $ ./result/bin/nixos-test-driver starting VDE switch for network 1 > You can then take any Perl statement, e.g. > startAll > testScript > $machine->succeed("touch /tmp/foo") The function testScript executes the entire test script and drops you back into the test driver command line upon its completion. This allows you to inspect the state of the VMs after the test (e.g. to debug the test script). To just start and experiment with the VMs, run: $ nix-build nixos/tests/login.nix -A driver $ ./result/bin/nixos-run-vms The script nixos-run-vms starts the virtual machines defined by test. The root file system of the VMs is created on the fly and kept across VM restarts in ./hostname.qcow2.