mirror of
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Update section on writing tests
This commit is contained in:
Eelco Dolstra
parent
29027fd1e1
commit
e1a1146690
@ -1,5 +1,6 @@
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<chapter xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink">
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xml:id="ch-development">
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<title>Development</title>
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@ -9,7 +10,7 @@ NixOS.</para>
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<!--===============================================================-->
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<section>
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<section xml:id="sec-getting-sources">
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<title>Getting the sources</title>
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@ -74,7 +75,7 @@ in <filename>nixos/</filename> as packages.</para>
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<!--===============================================================-->
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<section>
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<section xml:id="sec-writing-modules">
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<title>Writing NixOS modules</title>
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@ -579,7 +580,7 @@ systemd.services.dhcpcd =
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<!--===============================================================-->
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<section>
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<section xml:id="sec-building-parts">
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<title>Building specific parts of NixOS</title>
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@ -692,7 +693,7 @@ $ systemctl start tmp-httpd.service
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<!--===============================================================-->
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<section>
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<section xml:id="sec-building-cd">
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<title>Building your own NixOS CD</title>
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@ -748,57 +749,310 @@ $ ./result/bin/nixos-install</screen>
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<!--===============================================================-->
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<section><title>Whole-system testing using virtual machines</title>
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<section xml:id="sec-nixos-tests">
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<para>Complete NixOS GNU/Linux systems can be tested in virtual
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machines (VMs). This makes it possible to test a system upgrade or
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configuration change before rebooting into it, using the
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<command>nixos-rebuild build-vm</command> or <command>nixos-rebuild
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build-vm-with-bootloader</command> command.</para>
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<title>NixOS tests</title>
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<!-- The following is adapted from
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http://wiki.nixos.org/wiki/NixOS_VM_tests, by Eelco Dolstra. -->
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<para>The <filename>tests/</filename> directory in the NixOS source
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tree contains several <emphasis>whole-system unit tests</emphasis>.
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These tests can be run<footnote><para>NixOS tests can be run both from
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NixOS and from a non-NixOS GNU/Linux distribution, provided the Nix
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package manager is installed.</para></footnote> from the NixOS source
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tree as follows:
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<para>When you add some feature to NixOS, you should write a test for
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it. NixOS tests are kept in the directory <filename
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xlink:href="https://github.com/NixOS/nixpkgs/tree/master/nixos/tests">nixos/tests</filename>,
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and are executed (using Nix) by a testing framework that automatically
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starts one or more virtual machines containing the NixOS system(s)
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required for the test.</para>
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<simplesect><title>Writing tests</title>
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<para>A NixOS test is a Nix expression that has the following structure:
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<programlisting>
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import ./make-test.nix {
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# Either the configuration of a single machine:
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machine =
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{ config, pkgs, ... }:
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{ <replaceable>configuration…</replaceable>
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};
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# Or a set of machines:
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nodes =
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{ <replaceable>machine1</replaceable> =
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{ config, pkgs, ... }: { <replaceable>…</replaceable> };
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<replaceable>machine2</replaceable> =
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{ config, pkgs, ... }: { <replaceable>…</replaceable> };
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…
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};
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testScript =
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''
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<replaceable>Perl code…</replaceable>
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'';
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}
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</programlisting>
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The attribute <literal>testScript</literal> is a bit of Perl code that
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executes the test (described below). During the test, it will start
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one or more virtual machines, the configuration of which is described
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by the attribute <literal>machine</literal> (if you need only one
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machine in your test) or by the attribute <literal>nodes</literal> (if
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you need multiple machines). For instance, <filename
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xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/tests/login.nix">login.nix</filename>
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only needs a single machine to test whether users can log in on the
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virtual console, whether device ownership is correctly maintained when
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switching between consoles, and so on. On the other hand, <filename
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xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/tests/nfs.nix">nfs.nix</filename>,
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which tests NFS client and server functionality in the Linux kernel
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(including whether locks are maintained across server crashes),
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requires three machines: a server and two clients.</para>
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<para>There are a few special NixOS configuration options for test
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VMs:
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<!-- FIXME: would be nice to generate this automatically. -->
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<variablelist>
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<varlistentry>
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<term><option>virtualisation.memorySize</option></term>
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<listitem><para>The memory of the VM in
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megabytes.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>virtualisation.vlans</option></term>
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<listitem><para>The virtual networks to which the VM is
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connected. See <filename
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xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/tests/nat.nix">nat.nix</filename>
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for an example.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>virtualisation.writableStore</option></term>
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<listitem><para>By default, the Nix store in the VM is not
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writable. If you enable this option, a writable union file system
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is mounted on top of the Nix store to make it appear
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writable. This is necessary for tests that run Nix operations that
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modify the store.</para></listitem>
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</varlistentry>
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</variablelist>
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For more options, see the module <filename
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xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/virtualisation/qemu-vm.nix">qemu-vm.nix</filename>.</para>
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<para>The test script is a sequence of Perl statements that perform
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various actions, such as starting VMs, executing commands in the VMs,
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and so on. Each virtual machine is represented as an object stored in
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the variable <literal>$<replaceable>name</replaceable></literal>,
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where <replaceable>name</replaceable> is the identifier of the machine
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(which is just <literal>machine</literal> if you didn’t specify
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multiple machines using the <literal>nodes</literal> attribute). For
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instance, the following starts the machine, waits until it has
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finished booting, then executes a command and checks that the output
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is more-or-less correct:
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<programlisting>
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$machine->start;
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$machine->waitForUnit("default.target");
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$machine->succeed("uname") =~ /Linux/;
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</programlisting>
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The first line is actually unnecessary; machines are implicitly
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started when you first execute an action on them (such as
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<literal>waitForUnit</literal> or <literal>succeed</literal>). If you
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have multiple machines, you can speed up the test by starting them in
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parallel:
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<programlisting>
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startAll;
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</programlisting>
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</para>
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<para>The following methods are available on machine objects:
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<variablelist>
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<varlistentry>
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<term><methodname>start</methodname></term>
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<listitem><para>Start the virtual machine. This method is
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asynchronous — it does not wait for the machine to finish
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booting.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><methodname>shutdown</methodname></term>
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<listitem><para>Shut down the machine, waiting for the VM to
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exit.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><methodname>crash</methodname></term>
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<listitem><para>Simulate a sudden power failure, by telling the VM
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to exit immediately.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><methodname>block</methodname></term>
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<listitem><para>Simulate unplugging the Ethernet cable that
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connects the machine to the other machines.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><methodname>unblock</methodname></term>
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<listitem><para>Undo the effect of
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<methodname>block</methodname>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><methodname>screenshot</methodname></term>
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<listitem><para>Take a picture of the display of the virtual
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machine, in PNG format. The screenshot is linked from the HTML
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log.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><methodname>sendMonitorCommand</methodname></term>
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<listitem><para>Send a command to the QEMU monitor. This is rarely
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used, but allows doing stuff such as attaching virtual USB disks
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to a running machine.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><methodname>sendKeys</methodname></term>
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<listitem><para>Simulate pressing keys on the virtual keyboard,
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e.g., <literal>sendKeys("ctrl-alt-delete")</literal>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><methodname>sendChars</methodname></term>
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<listitem><para>Simulate typing a sequence of characters on the
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virtual keyboard, e.g., <literal>sendKeys("foobar\n")</literal>
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will type the string <literal>foobar</literal> followed by the
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Enter key.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><methodname>execute</methodname></term>
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<listitem><para>Execute a shell command, returning a list
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<literal>(<replaceable>status</replaceable>,
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<replaceable>stdout</replaceable>)</literal>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><methodname>succeed</methodname></term>
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<listitem><para>Execute a shell command, raising an exception if
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the exit status is not zero, otherwise returning the standard
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output.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><methodname>fail</methodname></term>
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<listitem><para>Like <methodname>succeed</methodname>, but raising
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an exception if the command returns a zero status.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><methodname>waitUntilSucceeds</methodname></term>
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<listitem><para>Repeat a shell command with 1-second intervals
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until it succeeds.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><methodname>waitUntilFails</methodname></term>
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<listitem><para>Repeat a shell command with 1-second intervals
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until it fails.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><methodname>waitForUnit</methodname></term>
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<listitem><para>Wait until the specified systemd unit has reached
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the “active” state.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><methodname>waitForFile</methodname></term>
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<listitem><para>Wait until the specified file
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exists.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><methodname>waitForOpenPort</methodname></term>
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<listitem><para>Wait until a process is listening on the given TCP
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port (on <literal>localhost</literal>, at least).</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><methodname>waitForClosedPort</methodname></term>
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<listitem><para>Wait until nobody is listening on the given TCP
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port.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><methodname>waitForX</methodname></term>
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<listitem><para>Wait until the X11 server is accepting
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connections.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><methodname>waitForWindow</methodname></term>
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<listitem><para>Wait until an X11 window has appeared whose name
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matches the given regular expression, e.g.,
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<literal>waitForWindow(qr/Terminal/)</literal>.</para></listitem>
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</varlistentry>
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</variablelist>
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</para>
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</simplesect>
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<simplesect><title>Running tests</title>
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<para>You can run tests using <command>nix-build</command>. For
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example, to run the test <filename
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xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/tests/login.nix">login.nix</filename>,
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you just do:
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<screen>
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$ nix-build tests/ -A nfs.test
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$ nix-build '<nixpkgs/nixos/tests/login.nix>'
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</screen>
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This performs an automated test of the NFS client and server
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functionality in the Linux kernel, including file locking semantics
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(e.g., whether locks are maintained across server crashes). It will
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first build or download all the dependencies of the test (e.g., all
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packages needed to run a NixOS VM). The test is defined in <link
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xlink:href="https://nixos.org/repos/nix/nixos/trunk/tests/nfs.nix">
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<filename>tests/nfs.nix</filename></link>. If the test succeeds,
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<command>nix-build</command> will place a symlink
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<filename>./result</filename> in the current directory pointing at the
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location in the Nix store of the test results (e.g., screenshots, test
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reports, and so on). In particular, a pretty-printed log of the test
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is written to <filename>log.html</filename>, which can be viewed using
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a web browser like this:
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or, if you don’t want to rely on <envar>NIX_PATH</envar>:
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<screen>
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$ cd /my/nixpkgs/nixos/tests
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$ nix-build login.nix
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…
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running the VM test script
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machine: QEMU running (pid 8841)
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…
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6 out of 6 tests succeeded
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</screen>
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After building/downloading all required dependencies, this will
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perform a build that starts a QEMU/KVM virtual machine containing a
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NixOS system. The virtual machine mounts the Nix store of the host;
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this makes VM creation very fast, as no disk image needs to be
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created. Afterwards, you can view a pretty-printed log of the test:
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<screen>
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$ firefox result/log.html
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</screen>
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</para>
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<para>It is also possible to run the test environment interactively,
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allowing you to experiment with the VMs. For example:
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<screen>
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$ nix-build tests/ -A nfs.driver
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$ nix-build login.nix -A driver
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$ ./result/bin/nixos-run-vms
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</screen>
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The script <command>nixos-run-vms</command> starts the three virtual
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machines defined in the NFS test using QEMU/KVM. The root file system
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of the VMs is created on the fly and kept across VM restarts in
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The script <command>nixos-run-vms</command> starts the virtual
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machines defined by test. The root file system of the VMs is created
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on the fly and kept across VM restarts in
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<filename>./</filename><varname>hostname</varname><filename>.qcow2</filename>.</para>
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<para>Finally, the test itself can be run interactively. This is
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@ -811,17 +1065,11 @@ starting VDE switch for network 1
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>
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</screen>
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Perl statements can now be typed in to start or manipulate the VMs:
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You can then take any Perl statement, e.g.
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<screen>
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> startAll;
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(the VMs start booting)
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> $server->waitForJob("nfs-kernel-nfsd");
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> $client1->succeed("flock -x /data/lock -c 'sleep 100000' &");
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> $client2->fail("flock -n -s /data/lock true");
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> $client1->shutdown;
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(this releases client1's lock)
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> $client2->succeed("flock -n -s /data/lock true");
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> startAll
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> $machine->succeed("touch /tmp/foo")
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</screen>
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The function <command>testScript</command> executes the entire test
|
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@ -829,54 +1077,7 @@ script and drops you back into the test driver command line upon its
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completion. This allows you to inspect the state of the VMs after the
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test (e.g. to debug the test script).</para>
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||||
|
||||
<para>This and other tests are continuously run on <link
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xlink:href="http://hydra.nixos.org/jobset/nixos/trunk">the Hydra
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instance at <literal>nixos.org</literal></link>, which allows
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||||
developers to be notified of any regressions introduced by a NixOS or
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Nixpkgs change.</para>
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|
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<para>The actual Nix programming interface to VM testing is in NixOS,
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under <link
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||||
xlink:href="https://nixos.org/repos/nix/nixos/trunk/lib/testing.nix">
|
||||
<filename>lib/testing.nix</filename></link>. This file defines a
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function which takes an attribute set containing a
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<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
|
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which the main entry point is <literal>makeTest</literal>.
|
||||
</para>
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||||
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<para>The <literal>makeTest</literal> function takes a function
|
||||
similar to that found in <link
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||||
xlink:href="https://nixos.org/repos/nix/nixos/trunk/tests/nfs.nix">
|
||||
<filename>tests/nfs.nix</filename></link> (discussed above). It
|
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returns an attribute set containing (among others):
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||||
|
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<variablelist>
|
||||
|
||||
<varlistentry>
|
||||
<term><varname>test</varname></term>
|
||||
<listitem><para>A derivation containing the test log as an HTML
|
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file, as seen above, suitable for presentation in the Hydra
|
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continuous build system.</para></listitem>
|
||||
</varlistentry>
|
||||
|
||||
<varlistentry>
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||||
<term><varname>report</varname></term>
|
||||
<listitem><para>A derivation containing a code coverage report, with
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||||
meta-data suitable for Hydra.</para></listitem>
|
||||
</varlistentry>
|
||||
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<varlistentry>
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||||
<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>
|
||||
|
||||
|
||||
@ -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>
|
||||
|
||||
|
||||
Loading…
Reference in New Issue
Block a user