Update section on writing tests

This commit is contained in:
Eelco Dolstra 2014-04-14 19:07:35 +02:00
parent 29027fd1e1
commit e1a1146690
2 changed files with 296 additions and 95 deletions

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@ -1,5 +1,6 @@
<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink">
xmlns:xlink="http://www.w3.org/1999/xlink"
xml:id="ch-development">
<title>Development</title>
@ -9,7 +10,7 @@ NixOS.</para>
<!--===============================================================-->
<section>
<section xml:id="sec-getting-sources">
<title>Getting the sources</title>
@ -74,7 +75,7 @@ in <filename>nixos/</filename> as packages.</para>
<!--===============================================================-->
<section>
<section xml:id="sec-writing-modules">
<title>Writing NixOS modules</title>
@ -579,7 +580,7 @@ systemd.services.dhcpcd =
<!--===============================================================-->
<section>
<section xml:id="sec-building-parts">
<title>Building specific parts of NixOS</title>
@ -692,7 +693,7 @@ $ systemctl start tmp-httpd.service
<!--===============================================================-->
<section>
<section xml:id="sec-building-cd">
<title>Building your own NixOS CD</title>
@ -748,57 +749,310 @@ $ ./result/bin/nixos-install</screen>
<!--===============================================================-->
<section><title>Whole-system testing using virtual machines</title>
<section xml:id="sec-nixos-tests">
<para>Complete NixOS GNU/Linux systems can be tested in virtual
machines (VMs). This makes it possible to test a system upgrade or
configuration change before rebooting into it, using the
<command>nixos-rebuild build-vm</command> or <command>nixos-rebuild
build-vm-with-bootloader</command> command.</para>
<title>NixOS tests</title>
<!-- The following is adapted from
http://wiki.nixos.org/wiki/NixOS_VM_tests, by Eelco Dolstra. -->
<para>The <filename>tests/</filename> directory in the NixOS source
tree contains several <emphasis>whole-system unit tests</emphasis>.
These tests can be run<footnote><para>NixOS tests can be run both from
NixOS and from a non-NixOS GNU/Linux distribution, provided the Nix
package manager is installed.</para></footnote> from the NixOS source
tree as follows:
<para>When you add some feature to NixOS, you should write a test for
it. NixOS tests are kept in the directory <filename
xlink:href="https://github.com/NixOS/nixpkgs/tree/master/nixos/tests">nixos/tests</filename>,
and are executed (using Nix) by a testing framework that automatically
starts one or more virtual machines containing the NixOS system(s)
required for the test.</para>
<simplesect><title>Writing tests</title>
<para>A NixOS test is a Nix expression that has the following structure:
<programlisting>
import ./make-test.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>Perl code…</replaceable>
'';
}
</programlisting>
The attribute <literal>testScript</literal> is a bit of Perl 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.nix">nfs.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 Perl 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>,
where <replaceable>name</replaceable> is the identifier of the machine
(which is just <literal>machine</literal> if you didnt specify
multiple machines using the <literal>nodes</literal> attribute). For
instance, the following 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->waitForUnit("default.target");
$machine->succeed("uname") =~ /Linux/;
</programlisting>
The first line is actually unnecessary; machines are implicitly
started when you first execute an action on them (such as
<literal>waitForUnit</literal> or <literal>succeed</literal>). If you
have multiple machines, you can speed up the test by starting them in
parallel:
<programlisting>
startAll;
</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>sendMonitorCommand</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>sendKeys</methodname></term>
<listitem><para>Simulate pressing keys on the virtual keyboard,
e.g., <literal>sendKeys("ctrl-alt-delete")</literal>.</para></listitem>
</varlistentry>
<varlistentry>
<term><methodname>sendChars</methodname></term>
<listitem><para>Simulate typing a sequence of characters on the
virtual keyboard, e.g., <literal>sendKeys("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.</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>waitUntilSucceeds</methodname></term>
<listitem><para>Repeat a shell command with 1-second intervals
until it succeeds.</para></listitem>
</varlistentry>
<varlistentry>
<term><methodname>waitUntilFails</methodname></term>
<listitem><para>Repeat a shell command with 1-second intervals
until it fails.</para></listitem>
</varlistentry>
<varlistentry>
<term><methodname>waitForUnit</methodname></term>
<listitem><para>Wait until the specified systemd unit has reached
the “active” state.</para></listitem>
</varlistentry>
<varlistentry>
<term><methodname>waitForFile</methodname></term>
<listitem><para>Wait until the specified file
exists.</para></listitem>
</varlistentry>
<varlistentry>
<term><methodname>waitForOpenPort</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>waitForClosedPort</methodname></term>
<listitem><para>Wait until nobody is listening on the given TCP
port.</para></listitem>
</varlistentry>
<varlistentry>
<term><methodname>waitForX</methodname></term>
<listitem><para>Wait until the X11 server is accepting
connections.</para></listitem>
</varlistentry>
<varlistentry>
<term><methodname>waitForWindow</methodname></term>
<listitem><para>Wait until an X11 window has appeared whose name
matches the given regular expression, e.g.,
<literal>waitForWindow(qr/Terminal/)</literal>.</para></listitem>
</varlistentry>
</variablelist>
</para>
</simplesect>
<simplesect><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>
$ nix-build tests/ -A nfs.test
$ nix-build '&lt;nixpkgs/nixos/tests/login.nix>'
</screen>
This performs an automated test of the NFS client and server
functionality in the Linux kernel, including file locking semantics
(e.g., whether locks are maintained across server crashes). It will
first build or download all the dependencies of the test (e.g., all
packages needed to run a NixOS VM). The test is defined in <link
xlink:href="https://nixos.org/repos/nix/nixos/trunk/tests/nfs.nix">
<filename>tests/nfs.nix</filename></link>. If the test succeeds,
<command>nix-build</command> will place a symlink
<filename>./result</filename> in the current directory pointing at the
location in the Nix store of the test results (e.g., screenshots, test
reports, and so on). In particular, a pretty-printed log of the test
is written to <filename>log.html</filename>, which can be viewed using
a web browser like this:
or, if you dont want to rely on <envar>NIX_PATH</envar>:
<screen>
$ 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
</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>
$ firefox result/log.html
</screen>
</para>
<para>It is also possible to run the test environment interactively,
allowing you to experiment with the VMs. For example:
<screen>
$ nix-build tests/ -A nfs.driver
$ nix-build login.nix -A driver
$ ./result/bin/nixos-run-vms
</screen>
The script <command>nixos-run-vms</command> starts the three virtual
machines defined in the NFS test using QEMU/KVM. The root file system
of the VMs is created on the fly and kept across VM restarts in
The script <command>nixos-run-vms</command> 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
<filename>./</filename><varname>hostname</varname><filename>.qcow2</filename>.</para>
<para>Finally, the test itself can be run interactively. This is
@ -811,17 +1065,11 @@ starting VDE switch for network 1
&gt;
</screen>
Perl statements can now be typed in to start or manipulate the VMs:
You can then take any Perl statement, e.g.
<screen>
&gt; startAll;
(the VMs start booting)
&gt; $server-&gt;waitForJob("nfs-kernel-nfsd");
&gt; $client1-&gt;succeed("flock -x /data/lock -c 'sleep 100000' &amp;");
&gt; $client2-&gt;fail("flock -n -s /data/lock true");
&gt; $client1-&gt;shutdown;
(this releases client1's lock)
&gt; $client2-&gt;succeed("flock -n -s /data/lock true");
&gt; startAll
&gt; $machine->succeed("touch /tmp/foo")
</screen>
The function <command>testScript</command> executes the entire test
@ -829,54 +1077,7 @@ 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>This and other tests are continuously run on <link
xlink:href="http://hydra.nixos.org/jobset/nixos/trunk">the Hydra
instance at <literal>nixos.org</literal></link>, which allows
developers to be notified of any regressions introduced by a NixOS or
Nixpkgs change.</para>
<para>The actual Nix programming interface to VM testing is in NixOS,
under <link
xlink:href="https://nixos.org/repos/nix/nixos/trunk/lib/testing.nix">
<filename>lib/testing.nix</filename></link>. This file defines a
function which takes an attribute set containing a
<literal>nixpkgs</literal> attribute (the path to a Nixpkgs checkout),
and a <literal>system</literal> attribute (the system type). It
returns an attribute set containing several utility functions, among
which the main entry point is <literal>makeTest</literal>.
</para>
<para>The <literal>makeTest</literal> function takes a function
similar to that found in <link
xlink:href="https://nixos.org/repos/nix/nixos/trunk/tests/nfs.nix">
<filename>tests/nfs.nix</filename></link> (discussed above). It
returns an attribute set containing (among others):
<variablelist>
<varlistentry>
<term><varname>test</varname></term>
<listitem><para>A derivation containing the test log as an HTML
file, as seen above, suitable for presentation in the Hydra
continuous build system.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>report</varname></term>
<listitem><para>A derivation containing a code coverage report, with
meta-data suitable for Hydra.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>driver</varname></term>
<listitem><para>A derivation containing scripts to run the VM test or
interact with the VM network interactively, as seen above.</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</simplesect>
</section>

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@ -60,7 +60,7 @@
<xi:include href="release-notes.xml" />
<appendix xml:id="ch-options">
<title>List of options</title>
<title>Configuration options</title>
<xi:include href="options-db.xml" />
</appendix>