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nixos/doc: convert "Chapter 62. NixOS Tests" to CommonMark
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6
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@ -13,7 +13,7 @@ xlink:href="https://github.com/NixOS/nixpkgs/tree/master/nixos/tests">nixos/test
one or more virtual machines containing the NixOS system(s) required for the
test.
</para>
<xi:include href="writing-nixos-tests.xml" />
<xi:include href="running-nixos-tests.xml" />
<xi:include href="running-nixos-tests-interactively.xml" />
<xi:include href="../from_md/development/writing-nixos-tests.section.xml" />
<xi:include href="../from_md/development/running-nixos-tests.section.xml" />
<xi:include href="../from_md/development/running-nixos-tests-interactively.section.xml" />
</chapter>

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# Running Tests interactively {#sec-running-nixos-tests-interactively}
The test itself can be run interactively. This is particularly useful
when developing or debugging a test:
```ShellSession
$ nix-build nixos/tests/login.nix -A driverInteractive
$ ./result/bin/nixos-test-driver
starting VDE switch for network 1
>
```
You can then take any Python statement, e.g.
```py
> start_all()
> test_script()
> machine.succeed("touch /tmp/foo")
> print(machine.succeed("pwd")) # Show stdout of command
```
The function `test_script` 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:
```ShellSession
$ nix-build nixos/tests/login.nix -A driverInteractive
$ ./result/bin/nixos-run-vms
```
The script `nixos-run-vms` starts the virtual machines defined by test.
You can re-use the VM states coming from a previous run by setting the
`--keep-vm-state` flag.
```ShellSession
$ ./result/bin/nixos-run-vms --keep-vm-state
```
The machine state is stored in the `$TMPDIR/vm-state-machinename`
directory.

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<section xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xmlns:xi="http://www.w3.org/2001/XInclude"
version="5.0"
xml:id="sec-running-nixos-tests-interactively">
<title>Running Tests interactively</title>
<para>
The test itself can be run interactively. This is particularly useful when
developing or debugging a test:
<screen>
<prompt>$ </prompt>nix-build nixos/tests/login.nix -A driverInteractive
<prompt>$ </prompt>./result/bin/nixos-test-driver
starting VDE switch for network 1
<prompt>&gt;</prompt>
</screen>
You can then take any Python statement, e.g.
<screen>
<prompt>&gt;</prompt> start_all()
<prompt>&gt;</prompt> test_script()
<prompt>&gt;</prompt> machine.succeed("touch /tmp/foo")
<prompt>&gt;</prompt> print(machine.succeed("pwd")) # Show stdout of command
</screen>
The function <command>test_script</command> 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).
</para>
<para>
To just start and experiment with the VMs, run:
<screen>
<prompt>$ </prompt>nix-build nixos/tests/login.nix -A driverInteractive
<prompt>$ </prompt>./result/bin/nixos-run-vms
</screen>
The script <command>nixos-run-vms</command> starts the virtual machines
defined by test.
</para>
<para>
You can re-use the VM states coming from a previous run
by setting the <command>--keep-vm-state</command> flag.
<screen>
<prompt>$ </prompt>./result/bin/nixos-run-vms --keep-vm-state
</screen>
The machine state is stored in the
<filename>$TMPDIR/vm-state-</filename><varname>machinename</varname> directory.
</para>
</section>

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# Running Tests {#sec-running-nixos-tests}
You can run tests using `nix-build`. For example, to run the test
[`login.nix`](https://github.com/NixOS/nixpkgs/blob/master/nixos/tests/login.nix),
you just do:
```ShellSession
$ nix-build '<nixpkgs/nixos/tests/login.nix>'
```
or, if you don't want to rely on `NIX_PATH`:
```ShellSession
$ 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:
```ShellSession
$ firefox result/log.html
```

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<section xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xmlns:xi="http://www.w3.org/2001/XInclude"
version="5.0"
xml:id="sec-running-nixos-tests">
<title>Running Tests</title>
<para>
You can run tests using <command>nix-build</command>. For example, to run the
test
<filename
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/tests/login.nix">login.nix</filename>,
you just do:
<screen>
<prompt>$ </prompt>nix-build '&lt;nixpkgs/nixos/tests/login.nix>'
</screen>
or, if you don’t want to rely on <envar>NIX_PATH</envar>:
<screen>
<prompt>$ </prompt>cd /my/nixpkgs/nixos/tests
<prompt>$ </prompt>nix-build login.nix
…
running the VM test script
machine: QEMU running (pid 8841)
…
6 out of 6 tests succeeded
</screen>
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:
<screen>
<prompt>$ </prompt>firefox result/log.html
</screen>
</para>
</section>

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# Writing Tests {#sec-writing-nixos-tests}
A NixOS test is a Nix expression that has the following structure:
```nix
import ./make-test-python.nix {
# Either the configuration of a single machine:
machine =
{ config, pkgs, ... }:
{ configuration…
};
# Or a set of machines:
nodes =
{ machine1 =
{ config, pkgs, ... }: { … };
machine2 =
{ config, pkgs, ... }: { … };
…
};
testScript =
''
Python code…
'';
}
```
The attribute `testScript` is a bit of Python code that executes the
test (described below). During the test, it will start one or more
virtual machines, the configuration of which is described by the
attribute `machine` (if you need only one machine in your test) or by
the attribute `nodes` (if you need multiple machines). For instance,
[`login.nix`](https://github.com/NixOS/nixpkgs/blob/master/nixos/tests/login.nix)
only needs a single machine to test whether users can log in
on the virtual console, whether device ownership is correctly maintained
when switching between consoles, and so on. On the other hand,
[`nfs/simple.nix`](https://github.com/NixOS/nixpkgs/blob/master/nixos/tests/nfs/simple.nix),
which tests NFS client and server functionality in the
Linux kernel (including whether locks are maintained across server
crashes), requires three machines: a server and two clients.
There are a few special NixOS configuration options for test VMs:
`virtualisation.memorySize`
: The memory of the VM in megabytes.
`virtualisation.vlans`
: The virtual networks to which the VM is connected. See
[`nat.nix`](https://github.com/NixOS/nixpkgs/blob/master/nixos/tests/nat.nix)
for an example.
`virtualisation.writableStore`
: By default, the Nix store in the VM is not writable. If you enable
this option, a writable union file system is mounted on top of the
Nix store to make it appear writable. This is necessary for tests
that run Nix operations that modify the store.
For more options, see the module
[`qemu-vm.nix`](https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/virtualisation/qemu-vm.nix).
The test script is a sequence of Python statements that perform various
actions, such as starting VMs, executing commands in the VMs, and so on.
Each virtual machine is represented as an object stored in the variable
`name` if this is also the identifier of the machine in the declarative
config. If you didn\'t specify multiple machines using the `nodes`
attribute, it is just `machine`. The following example starts the
machine, waits until it has finished booting, then executes a command
and checks that the output is more-or-less correct:
```py
machine.start()
machine.wait_for_unit("default.target")
if not "Linux" in machine.succeed("uname"):
raise Exception("Wrong OS")
```
The first line is actually unnecessary; machines are implicitly started
when you first execute an action on them (such as `wait_for_unit` or
`succeed`). If you have multiple machines, you can speed up the test by
starting them in parallel:
```py
start_all()
```
The following methods are available on machine objects:
`start`
: Start the virtual machine. This method is asynchronous --- it does
not wait for the machine to finish booting.
`shutdown`
: Shut down the machine, waiting for the VM to exit.
`crash`
: Simulate a sudden power failure, by telling the VM to exit
immediately.
`block`
: Simulate unplugging the Ethernet cable that connects the machine to
the other machines.
`unblock`
: Undo the effect of `block`.
`screenshot`
: Take a picture of the display of the virtual machine, in PNG format.
The screenshot is linked from the HTML log.
`get_screen_text_variants`
: Return a list of different interpretations of what is currently
visible on the machine\'s screen using optical character
recognition. The number and order of the interpretations is not
specified and is subject to change, but if no exception is raised at
least one will be returned.
::: {.note}
This requires passing `enableOCR` to the test attribute set.
:::
`get_screen_text`
: Return a textual representation of what is currently visible on the
machine\'s screen using optical character recognition.
::: {.note}
This requires passing `enableOCR` to the test attribute set.
:::
`send_monitor_command`
: Send a command to the QEMU monitor. This is rarely used, but allows
doing stuff such as attaching virtual USB disks to a running
machine.
`send_key`
: Simulate pressing keys on the virtual keyboard, e.g.,
`send_key("ctrl-alt-delete")`.
`send_chars`
: Simulate typing a sequence of characters on the virtual keyboard,
e.g., `send_chars("foobar\n")` will type the string `foobar`
followed by the Enter key.
`execute`
: Execute a shell command, returning a list `(status, stdout)`.
`succeed`
: Execute a shell command, raising an exception if the exit status is
not zero, otherwise returning the standard output. Commands are run
with `set -euo pipefail` set:
- If several commands are separated by `;` and one fails, the
command as a whole will fail.
- For pipelines, the last non-zero exit status will be returned
(if there is one, zero will be returned otherwise).
- Dereferencing unset variables fail the command.
`fail`
: Like `succeed`, but raising an exception if the command returns a zero
status.
`wait_until_succeeds`
: Repeat a shell command with 1-second intervals until it succeeds.
`wait_until_fails`
: Repeat a shell command with 1-second intervals until it fails.
`wait_for_unit`
: Wait until the specified systemd unit has reached the "active"
state.
`wait_for_file`
: Wait until the specified file exists.
`wait_for_open_port`
: Wait until a process is listening on the given TCP port (on
`localhost`, at least).
`wait_for_closed_port`
: Wait until nobody is listening on the given TCP port.
`wait_for_x`
: Wait until the X11 server is accepting connections.
`wait_for_text`
: Wait until the supplied regular expressions matches the textual
contents of the screen by using optical character recognition (see
`get_screen_text` and `get_screen_text_variants`).
::: {.note}
This requires passing `enableOCR` to the test attribute set.
:::
`wait_for_console_text`
: Wait until the supplied regular expressions match a line of the
serial console output. This method is useful when OCR is not
possibile or accurate enough.
`wait_for_window`
: Wait until an X11 window has appeared whose name matches the given
regular expression, e.g., `wait_for_window("Terminal")`.
`copy_from_host`
: Copies a file from host to machine, e.g.,
`copy_from_host("myfile", "/etc/my/important/file")`.
The first argument is the file on the host. The file needs to be
accessible while building the nix derivation. The second argument is
the location of the file on the machine.
`systemctl`
: Runs `systemctl` commands with optional support for
`systemctl --user`
```py
machine.systemctl("list-jobs --no-pager") # runs `systemctl list-jobs --no-pager`
machine.systemctl("list-jobs --no-pager", "any-user") # spawns a shell for `any-user` and runs `systemctl --user list-jobs --no-pager`
```
`shell_interact`
: Allows you to directly interact with the guest shell. This should
only be used during test development, not in production tests.
Killing the interactive session with `Ctrl-d` or `Ctrl-c` also ends
the guest session.
To test user units declared by `systemd.user.services` the optional
`user` argument can be used:
```py
machine.start()
machine.wait_for_x()
machine.wait_for_unit("xautolock.service", "x-session-user")
```
This applies to `systemctl`, `get_unit_info`, `wait_for_unit`,
`start_job` and `stop_job`.
For faster dev cycles it\'s also possible to disable the code-linters
(this shouldn\'t be commited though):
```nix
import ./make-test-python.nix {
skipLint = true;
machine =
{ config, pkgs, ... }:
{ configuration…
};
testScript =
''
Python code…
'';
}
```
This will produce a Nix warning at evaluation time. To fully disable the
linter, wrap the test script in comment directives to disable the Black
linter directly (again, don\'t commit this within the Nixpkgs
repository):
```nix
testScript =
''
# fmt: off
Python code…
# fmt: on
'';
```

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<section xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xmlns:xi="http://www.w3.org/2001/XInclude"
version="5.0"
xml:id="sec-writing-nixos-tests">
<title>Writing Tests</title>
<para>
A NixOS test is a Nix expression that has the following structure:
<programlisting>
import ./make-test-python.nix {
# Either the configuration of a single machine:
machine =
{ config, pkgs, ... }:
{ <replaceable>configuration…</replaceable>
};
# Or a set of machines:
nodes =
{ <replaceable>machine1</replaceable> =
{ config, pkgs, ... }: { <replaceable>…</replaceable> };
<replaceable>machine2</replaceable> =
{ config, pkgs, ... }: { <replaceable>…</replaceable> };
…
};
testScript =
''
<replaceable>Python code…</replaceable>
'';
}
</programlisting>
The attribute <literal>testScript</literal> is a bit of Python code that
executes the test (described below). During the test, it will start one or
more virtual machines, the configuration of which is described by the
attribute <literal>machine</literal> (if you need only one machine in your
test) or by the attribute <literal>nodes</literal> (if you need multiple
machines). For instance,
<filename
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/tests/login.nix">login.nix</filename>
only needs a single machine to test whether users can log in on the virtual
console, whether device ownership is correctly maintained when switching
between consoles, and so on. On the other hand,
<filename
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/tests/nfs/simple.nix">nfs/simple.nix</filename>,
which tests NFS client and server functionality in the Linux kernel
(including whether locks are maintained across server crashes), requires
three machines: a server and two clients.
</para>
<para>
There are a few special NixOS configuration options for test VMs:
<!-- FIXME: would be nice to generate this automatically. -->
<variablelist>
<varlistentry>
<term>
<option>virtualisation.memorySize</option>
</term>
<listitem>
<para>
The memory of the VM in megabytes.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<option>virtualisation.vlans</option>
</term>
<listitem>
<para>
The virtual networks to which the VM is connected. See
<filename
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/tests/nat.nix">nat.nix</filename>
for an example.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<option>virtualisation.writableStore</option>
</term>
<listitem>
<para>
By default, the Nix store in the VM is not writable. If you enable this
option, a writable union file system is mounted on top of the Nix store
to make it appear writable. This is necessary for tests that run Nix
operations that modify the store.
</para>
</listitem>
</varlistentry>
</variablelist>
For more options, see the module
<filename
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/virtualisation/qemu-vm.nix">qemu-vm.nix</filename>.
</para>
<para>
The test script is a sequence of Python statements that perform various
actions, such as starting VMs, executing commands in the VMs, and so on. Each
virtual machine is represented as an object stored in the variable
<literal><replaceable>name</replaceable></literal> if this is also the
identifier of the machine in the declarative config.
If you didn't specify multiple machines using the <literal>nodes</literal>
attribute, it is just <literal>machine</literal>.
The following example starts the machine, waits until it has finished booting,
then executes a command and checks that the output is more-or-less correct:
<programlisting>
machine.start()
machine.wait_for_unit("default.target")
if not "Linux" in machine.succeed("uname"):
raise Exception("Wrong OS")
</programlisting>
The first line is actually unnecessary; machines are implicitly started when
you first execute an action on them (such as <literal>wait_for_unit</literal>
or <literal>succeed</literal>). If you have multiple machines, you can speed
up the test by starting them in parallel:
<programlisting>
start_all()
</programlisting>
</para>
<para>
The following methods are available on machine objects:
<variablelist>
<varlistentry>
<term>
<methodname>start</methodname>
</term>
<listitem>
<para>
Start the virtual machine. This method is asynchronous — it does not
wait for the machine to finish booting.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>shutdown</methodname>
</term>
<listitem>
<para>
Shut down the machine, waiting for the VM to exit.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>crash</methodname>
</term>
<listitem>
<para>
Simulate a sudden power failure, by telling the VM to exit immediately.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>block</methodname>
</term>
<listitem>
<para>
Simulate unplugging the Ethernet cable that connects the machine to the
other machines.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>unblock</methodname>
</term>
<listitem>
<para>
Undo the effect of <methodname>block</methodname>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>screenshot</methodname>
</term>
<listitem>
<para>
Take a picture of the display of the virtual machine, in PNG format. The
screenshot is linked from the HTML log.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>get_screen_text_variants</methodname>
</term>
<listitem>
<para>
Return a list of different interpretations of what is currently visible
on the machine's screen using optical character recognition. The number
and order of the interpretations is not specified and is subject to
change, but if no exception is raised at least one will be returned.
</para>
<note>
<para>
This requires passing <option>enableOCR</option> to the test attribute
set.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>get_screen_text</methodname>
</term>
<listitem>
<para>
Return a textual representation of what is currently visible on the
machine's screen using optical character recognition.
</para>
<note>
<para>
This requires passing <option>enableOCR</option> to the test attribute
set.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>send_monitor_command</methodname>
</term>
<listitem>
<para>
Send a command to the QEMU monitor. This is rarely used, but allows doing
stuff such as attaching virtual USB disks to a running machine.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>send_key</methodname>
</term>
<listitem>
<para>
Simulate pressing keys on the virtual keyboard, e.g.,
<literal>send_key("ctrl-alt-delete")</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>send_chars</methodname>
</term>
<listitem>
<para>
Simulate typing a sequence of characters on the virtual keyboard, e.g.,
<literal>send_chars("foobar\n")</literal> will type the string
<literal>foobar</literal> followed by the Enter key.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>execute</methodname>
</term>
<listitem>
<para>
Execute a shell command, returning a list
<literal>(<replaceable>status</replaceable>,
<replaceable>stdout</replaceable>)</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>succeed</methodname>
</term>
<listitem>
<para>
Execute a shell command, raising an exception if the exit status
is not zero, otherwise returning the standard output. Commands
are run with <literal>set -euo pipefail</literal> set:
<itemizedlist>
<listitem>
<para>
If several commands are separated by <literal>;</literal>
and one fails, the command as a whole will fail.
</para>
</listitem>
<listitem>
<para>
For pipelines, the last non-zero exit status will be
returned (if there is one, zero will be returned
otherwise).
</para>
</listitem>
<listitem>
<para>
Dereferencing unset variables fail the command.
</para>
</listitem>
</itemizedlist>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>fail</methodname>
</term>
<listitem>
<para>
Like <methodname>succeed</methodname>, but raising an exception if the
command returns a zero status.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>wait_until_succeeds</methodname>
</term>
<listitem>
<para>
Repeat a shell command with 1-second intervals until it succeeds.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>wait_until_fails</methodname>
</term>
<listitem>
<para>
Repeat a shell command with 1-second intervals until it fails.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>wait_for_unit</methodname>
</term>
<listitem>
<para>
Wait until the specified systemd unit has reached the “active” state.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>wait_for_file</methodname>
</term>
<listitem>
<para>
Wait until the specified file exists.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>wait_for_open_port</methodname>
</term>
<listitem>
<para>
Wait until a process is listening on the given TCP port (on
<literal>localhost</literal>, at least).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>wait_for_closed_port</methodname>
</term>
<listitem>
<para>
Wait until nobody is listening on the given TCP port.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>wait_for_x</methodname>
</term>
<listitem>
<para>
Wait until the X11 server is accepting connections.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>wait_for_text</methodname>
</term>
<listitem>
<para>
Wait until the supplied regular expressions matches the textual contents
of the screen by using optical character recognition (see
<methodname>get_screen_text</methodname> and
<methodname>get_screen_text_variants</methodname>).
</para>
<note>
<para>
This requires passing <option>enableOCR</option> to the test attribute
set.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>wait_for_console_text</methodname>
</term>
<listitem>
<para>
Wait until the supplied regular expressions match a line of the serial
console output. This method is useful when OCR is not possibile or
accurate enough.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>wait_for_window</methodname>
</term>
<listitem>
<para>
Wait until an X11 window has appeared whose name matches the given
regular expression, e.g., <literal>wait_for_window("Terminal")</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>copy_from_host</methodname>
</term>
<listitem>
<para>
Copies a file from host to machine, e.g.,
<literal>copy_from_host("myfile", "/etc/my/important/file")</literal>.
</para>
<para>
The first argument is the file on the host. The file needs to be
accessible while building the nix derivation. The second argument is the
location of the file on the machine.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>systemctl</methodname>
</term>
<listitem>
<para>
Runs <literal>systemctl</literal> commands with optional support for
<literal>systemctl --user</literal>
</para>
<para>
<programlisting>
machine.systemctl("list-jobs --no-pager") # runs `systemctl list-jobs --no-pager`
machine.systemctl("list-jobs --no-pager", "any-user") # spawns a shell for `any-user` and runs `systemctl --user list-jobs --no-pager`
</programlisting>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<methodname>shell_interact</methodname>
</term>
<listitem>
<para>
Allows you to directly interact with the guest shell.
This should only be used during test development, not in production tests.
Killing the interactive session with <literal>Ctrl-d</literal> or <literal>Ctrl-c</literal> also ends the guest session.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
To test user units declared by <literal>systemd.user.services</literal> the
optional <literal>user</literal> argument can be used:
<programlisting>
machine.start()
machine.wait_for_x()
machine.wait_for_unit("xautolock.service", "x-session-user")
</programlisting>
This applies to <literal>systemctl</literal>, <literal>get_unit_info</literal>,
<literal>wait_for_unit</literal>, <literal>start_job</literal> and
<literal>stop_job</literal>.
</para>
<para>
For faster dev cycles it's also possible to disable the code-linters (this shouldn't
be commited though):
<programlisting>
import ./make-test-python.nix {
skipLint = true;
machine =
{ config, pkgs, ... }:
{ <replaceable>configuration…</replaceable>
};
testScript =
''
<replaceable>Python code…</replaceable>
'';
}
</programlisting>
This will produce a Nix warning at evaluation time. To fully disable the
linter, wrap the test script in comment directives to disable the Black linter
directly (again, don't commit this within the Nixpkgs repository):
<programlisting>
testScript =
''
# fmt: off
<replaceable>Python code…</replaceable>
# fmt: on
'';
</programlisting>
</para>
</section>

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<section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-running-nixos-tests-interactively">
<title>Running Tests interactively</title>
<para>
The test itself can be run interactively. This is particularly
useful when developing or debugging a test:
</para>
<programlisting>
$ nix-build nixos/tests/login.nix -A driverInteractive
$ ./result/bin/nixos-test-driver
starting VDE switch for network 1
&gt;
</programlisting>
<para>
You can then take any Python statement, e.g.
</para>
<programlisting language="python">
&gt; start_all()
&gt; test_script()
&gt; machine.succeed(&quot;touch /tmp/foo&quot;)
&gt; print(machine.succeed(&quot;pwd&quot;)) # Show stdout of command
</programlisting>
<para>
The function <literal>test_script</literal> 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).
</para>
<para>
To just start and experiment with the VMs, run:
</para>
<programlisting>
$ nix-build nixos/tests/login.nix -A driverInteractive
$ ./result/bin/nixos-run-vms
</programlisting>
<para>
The script <literal>nixos-run-vms</literal> starts the virtual
machines defined by test.
</para>
<para>
You can re-use the VM states coming from a previous run by setting
the <literal>--keep-vm-state</literal> flag.
</para>
<programlisting>
$ ./result/bin/nixos-run-vms --keep-vm-state
</programlisting>
<para>
The machine state is stored in the
<literal>$TMPDIR/vm-state-machinename</literal> directory.
</para>
</section>

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<section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-running-nixos-tests">
<title>Running Tests</title>
<para>
You can run tests using <literal>nix-build</literal>. For example,
to run the test
<link xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/tests/login.nix"><literal>login.nix</literal></link>,
you just do:
</para>
<programlisting>
$ nix-build '&lt;nixpkgs/nixos/tests/login.nix&gt;'
</programlisting>
<para>
or, if you don’t want to rely on <literal>NIX_PATH</literal>:
</para>
<programlisting>
$ 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
</programlisting>
<para>
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:
</para>
<programlisting>
$ firefox result/log.html
</programlisting>
</section>

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<section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-writing-nixos-tests">
<title>Writing Tests</title>
<para>
A NixOS test is a Nix expression that has the following structure:
</para>
<programlisting language="bash">
import ./make-test-python.nix {
# Either the configuration of a single machine:
machine =
{ config, pkgs, ... }:
{ configuration…
};
# Or a set of machines:
nodes =
{ machine1 =
{ config, pkgs, ... }: { … };
machine2 =
{ config, pkgs, ... }: { … };
…
};
testScript =
''
Python code…
'';
}
</programlisting>
<para>
The attribute <literal>testScript</literal> is a bit of Python code
that executes the test (described below). During the test, it will
start one or more virtual machines, the configuration of which is
described by the attribute <literal>machine</literal> (if you need
only one machine in your test) or by the attribute
<literal>nodes</literal> (if you need multiple machines). For
instance,
<link xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/tests/login.nix"><literal>login.nix</literal></link>
only needs a single machine to test whether users can log in on the
virtual console, whether device ownership is correctly maintained
when switching between consoles, and so on. On the other hand,
<link xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/tests/nfs/simple.nix"><literal>nfs/simple.nix</literal></link>,
which tests NFS client and server functionality in the Linux kernel
(including whether locks are maintained across server crashes),
requires three machines: a server and two clients.
</para>
<para>
There are a few special NixOS configuration options for test VMs:
</para>
<variablelist>
<varlistentry>
<term>
<literal>virtualisation.memorySize</literal>
</term>
<listitem>
<para>
The memory of the VM in megabytes.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>virtualisation.vlans</literal>
</term>
<listitem>
<para>
The virtual networks to which the VM is connected. See
<link xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/tests/nat.nix"><literal>nat.nix</literal></link>
for an example.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>virtualisation.writableStore</literal>
</term>
<listitem>
<para>
By default, the Nix store in the VM is not writable. If you
enable this option, a writable union file system is mounted on
top of the Nix store to make it appear writable. This is
necessary for tests that run Nix operations that modify the
store.
</para>
</listitem>
</varlistentry>
</variablelist>
<para>
For more options, see the module
<link xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/virtualisation/qemu-vm.nix"><literal>qemu-vm.nix</literal></link>.
</para>
<para>
The test script is a sequence of Python statements that perform
various actions, such as starting VMs, executing commands in the
VMs, and so on. Each virtual machine is represented as an object
stored in the variable <literal>name</literal> if this is also the
identifier of the machine in the declarative config. If you didn't
specify multiple machines using the <literal>nodes</literal>
attribute, it is just <literal>machine</literal>. The following
example starts the machine, waits until it has finished booting,
then executes a command and checks that the output is more-or-less
correct:
</para>
<programlisting language="python">
machine.start()
machine.wait_for_unit(&quot;default.target&quot;)
if not &quot;Linux&quot; in machine.succeed(&quot;uname&quot;):
raise Exception(&quot;Wrong OS&quot;)
</programlisting>
<para>
The first line is actually unnecessary; machines are implicitly
started when you first execute an action on them (such as
<literal>wait_for_unit</literal> or <literal>succeed</literal>). If
you have multiple machines, you can speed up the test by starting
them in parallel:
</para>
<programlisting language="python">
start_all()
</programlisting>
<para>
The following methods are available on machine objects:
</para>
<variablelist>
<varlistentry>
<term>
<literal>start</literal>
</term>
<listitem>
<para>
Start the virtual machine. This method is asynchronous — it
does not wait for the machine to finish booting.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>shutdown</literal>
</term>
<listitem>
<para>
Shut down the machine, waiting for the VM to exit.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>crash</literal>
</term>
<listitem>
<para>
Simulate a sudden power failure, by telling the VM to exit
immediately.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>block</literal>
</term>
<listitem>
<para>
Simulate unplugging the Ethernet cable that connects the
machine to the other machines.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>unblock</literal>
</term>
<listitem>
<para>
Undo the effect of <literal>block</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>screenshot</literal>
</term>
<listitem>
<para>
Take a picture of the display of the virtual machine, in PNG
format. The screenshot is linked from the HTML log.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>get_screen_text_variants</literal>
</term>
<listitem>
<para>
Return a list of different interpretations of what is
currently visible on the machine's screen using optical
character recognition. The number and order of the
interpretations is not specified and is subject to change, but
if no exception is raised at least one will be returned.
</para>
<note>
<para>
This requires passing <literal>enableOCR</literal> to the
test attribute set.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>get_screen_text</literal>
</term>
<listitem>
<para>
Return a textual representation of what is currently visible
on the machine's screen using optical character recognition.
</para>
<note>
<para>
This requires passing <literal>enableOCR</literal> to the
test attribute set.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>send_monitor_command</literal>
</term>
<listitem>
<para>
Send a command to the QEMU monitor. This is rarely used, but
allows doing stuff such as attaching virtual USB disks to a
running machine.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>send_key</literal>
</term>
<listitem>
<para>
Simulate pressing keys on the virtual keyboard, e.g.,
<literal>send_key(&quot;ctrl-alt-delete&quot;)</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>send_chars</literal>
</term>
<listitem>
<para>
Simulate typing a sequence of characters on the virtual
keyboard, e.g.,
<literal>send_chars(&quot;foobar\n&quot;)</literal> will type
the string <literal>foobar</literal> followed by the Enter
key.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>execute</literal>
</term>
<listitem>
<para>
Execute a shell command, returning a list
<literal>(status, stdout)</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>succeed</literal>
</term>
<listitem>
<para>
Execute a shell command, raising an exception if the exit
status is not zero, otherwise returning the standard output.
Commands are run with <literal>set -euo pipefail</literal>
set:
</para>
<itemizedlist>
<listitem>
<para>
If several commands are separated by <literal>;</literal>
and one fails, the command as a whole will fail.
</para>
</listitem>
<listitem>
<para>
For pipelines, the last non-zero exit status will be
returned (if there is one, zero will be returned
otherwise).
</para>
</listitem>
<listitem>
<para>
Dereferencing unset variables fail the command.
</para>
</listitem>
</itemizedlist>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>fail</literal>
</term>
<listitem>
<para>
Like <literal>succeed</literal>, but raising an exception if
the command returns a zero status.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>wait_until_succeeds</literal>
</term>
<listitem>
<para>
Repeat a shell command with 1-second intervals until it
succeeds.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>wait_until_fails</literal>
</term>
<listitem>
<para>
Repeat a shell command with 1-second intervals until it fails.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>wait_for_unit</literal>
</term>
<listitem>
<para>
Wait until the specified systemd unit has reached the
<quote>active</quote> state.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>wait_for_file</literal>
</term>
<listitem>
<para>
Wait until the specified file exists.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>wait_for_open_port</literal>
</term>
<listitem>
<para>
Wait until a process is listening on the given TCP port (on
<literal>localhost</literal>, at least).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>wait_for_closed_port</literal>
</term>
<listitem>
<para>
Wait until nobody is listening on the given TCP port.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>wait_for_x</literal>
</term>
<listitem>
<para>
Wait until the X11 server is accepting connections.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>wait_for_text</literal>
</term>
<listitem>
<para>
Wait until the supplied regular expressions matches the
textual contents of the screen by using optical character
recognition (see <literal>get_screen_text</literal> and
<literal>get_screen_text_variants</literal>).
</para>
<note>
<para>
This requires passing <literal>enableOCR</literal> to the
test attribute set.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>wait_for_console_text</literal>
</term>
<listitem>
<para>
Wait until the supplied regular expressions match a line of
the serial console output. This method is useful when OCR is
not possibile or accurate enough.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>wait_for_window</literal>
</term>
<listitem>
<para>
Wait until an X11 window has appeared whose name matches the
given regular expression, e.g.,
<literal>wait_for_window(&quot;Terminal&quot;)</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>copy_from_host</literal>
</term>
<listitem>
<para>
Copies a file from host to machine, e.g.,
<literal>copy_from_host(&quot;myfile&quot;, &quot;/etc/my/important/file&quot;)</literal>.
</para>
<para>
The first argument is the file on the host. The file needs to
be accessible while building the nix derivation. The second
argument is the location of the file on the machine.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>systemctl</literal>
</term>
<listitem>
<para>
Runs <literal>systemctl</literal> commands with optional
support for <literal>systemctl --user</literal>
</para>
<programlisting language="python">
machine.systemctl(&quot;list-jobs --no-pager&quot;) # runs `systemctl list-jobs --no-pager`
machine.systemctl(&quot;list-jobs --no-pager&quot;, &quot;any-user&quot;) # spawns a shell for `any-user` and runs `systemctl --user list-jobs --no-pager`
</programlisting>
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>shell_interact</literal>
</term>
<listitem>
<para>
Allows you to directly interact with the guest shell. This
should only be used during test development, not in production
tests. Killing the interactive session with
<literal>Ctrl-d</literal> or <literal>Ctrl-c</literal> also
ends the guest session.
</para>
</listitem>
</varlistentry>
</variablelist>
<para>
To test user units declared by
<literal>systemd.user.services</literal> the optional
<literal>user</literal> argument can be used:
</para>
<programlisting language="python">
machine.start()
machine.wait_for_x()
machine.wait_for_unit(&quot;xautolock.service&quot;, &quot;x-session-user&quot;)
</programlisting>
<para>
This applies to <literal>systemctl</literal>,
<literal>get_unit_info</literal>, <literal>wait_for_unit</literal>,
<literal>start_job</literal> and <literal>stop_job</literal>.
</para>
<para>
For faster dev cycles it's also possible to disable the code-linters
(this shouldn't be commited though):
</para>
<programlisting language="bash">
import ./make-test-python.nix {
skipLint = true;
machine =
{ config, pkgs, ... }:
{ configuration…
};
testScript =
''
Python code…
'';
}
</programlisting>
<para>
This will produce a Nix warning at evaluation time. To fully disable
the linter, wrap the test script in comment directives to disable
the Black linter directly (again, don't commit this within the
Nixpkgs repository):
</para>
<programlisting language="bash">
testScript =
''
# fmt: off
Python code…
# fmt: on
'';
</programlisting>
</section>