The derivation's `outputHashMode` is set by default to recursive, so the `script` can output a directory as well.

All other attributes are passed through to [`mkDerivation`](#sec-using-stdenv),
including `nativeBuildInputs` to specify dependencies available to the `script`.

:::{.example #ex-tester-runCommand-nix}

# Run a command with network access

```nix
testers.runCommand {
  name = "access-the-internet";
  script = ''
    curl -o /dev/null https://example.com
    touch $out
  '';
  nativeBuildInputs = with pkgs; [
    cacert
    curl
  ];
}
```

:::

## `runNixOSTest` {#tester-runNixOSTest}

A helper function that behaves exactly like the NixOS `runTest`, except it also assigns this Nixpkgs package set as the `pkgs` of the test and makes the `nixpkgs.*` options read-only.

If your test is part of the Nixpkgs repository, or if you need a more general entrypoint, see ["Calling a test" in the NixOS manual](https://nixos.org/manual/nixos/stable/index.html#sec-calling-nixos-tests).

:::{.example #ex-runNixOSTest-hello}

# Run a NixOS test using `runNixOSTest`

```nix
pkgs.testers.runNixOSTest (
  { lib, ... }:
  {
    name = "hello";
    nodes.machine =
      { pkgs, ... }:
      {
        environment.systemPackages = [ pkgs.hello ];
      };
    testScript = ''
      machine.succeed("hello")
    '';
  }
)
```

:::

## `nixosTest` {#tester-nixosTest}

Run a NixOS VM network test using this evaluation of Nixpkgs.

NOTE: This function is primarily for external use. NixOS itself uses `make-test-python.nix` directly. Packages defined in Nixpkgs [reuse NixOS tests via `nixosTests`, plural](#ssec-nixos-tests-linking).

It is mostly equivalent to the function `import ./make-test-python.nix` from the [NixOS manual](https://nixos.org/nixos/manual/index.html#sec-nixos-tests), except that the current application of Nixpkgs (`pkgs`) will be used, instead of letting NixOS invoke Nixpkgs anew.

If a test machine needs to set NixOS options under `nixpkgs`, it must set only the `nixpkgs.pkgs` option.

### Parameter {#tester-nixosTest-parameter}

A [NixOS VM test network](https://nixos.org/nixos/manual/index.html#sec-nixos-tests), or path to it. Example:

```nix
{
  name = "my-test";
  nodes = {
    machine1 =
      {
        lib,
        pkgs,
        nodes,
        ...
      }:
      {
        environment.systemPackages = [ pkgs.hello ];
        services.foo.enable = true;
      };
    # machine2 = ...;
  };
  testScript = ''
    start_all()
    machine1.wait_for_unit("foo.service")
    machine1.succeed("hello | foo-send")
  '';
}
```

### Result {#tester-nixosTest-result}

A derivation that runs the VM test.

Notable attributes:

 * `nodes`: the evaluated NixOS configurations. Useful for debugging and exploring the configuration.

 * `driverInteractive`: a script that launches an interactive Python session in the context of the `testScript`.