.. _sec-running-nixos-tests:

Running Tests
~~~~~~~~~~~~~

You can run tests using :command:`nix-build`. For example, to run the
test
`login.nix <https://github.com/NixOS/nixpkgs/blob/master/nixos/tests/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