# Running Tests

You can run tests using `nix-build`. For example, to run the test `login.nix`, you just do:

    $ nix-build '<nixpkgs/nixos/tests/login.nix>'

or, if you don’t want to rely on `NIX_PATH`:

    $ cd /my/nixpkgs/nixos/tests
    $ nix-build login.nix
    …
    running the VM test script
    machine: QEMU running (pid 8841)
    …
    6 out of 6 tests succeeded

After building/downloading all required dependencies, this will perform a build that starts a QEMU/KVM virtual machine containing a NixOS system. The virtual machine mounts the Nix store of the host; this makes VM creation very fast, as no disk image needs to be created. Afterwards, you can view a pretty-printed log of the test:

    $ firefox result/log.html