279 lines
9.8 KiB
XML
279 lines
9.8 KiB
XML
<section xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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version="5.0"
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xml:id="sec-writing-nixos-tests">
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<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>getScreenText</methodname></term>
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<listitem><para>Return a textual representation of what is currently
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visible on the machine's screen using optical character
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recognition.</para>
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<note><para>This requires passing <option>enableOCR</option> to the test
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attribute set.</para></note></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>waitForText</methodname></term>
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<listitem><para>Wait until the supplied regular expressions matches
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the textual contents of the screen by using optical character recognition
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(see <methodname>getScreenText</methodname>).</para>
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<note><para>This requires passing <option>enableOCR</option> to the test
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attribute set.</para></note></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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<varlistentry>
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<term><methodname>copyFileFromHost</methodname></term>
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<listitem><para>Copies a file from host to machine, e.g.,
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<literal>copyFileFromHost("myfile", "/etc/my/important/file")</literal>.</para>
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<para>The first argument is the file on the host. The file needs to be
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accessible while building the nix derivation. The second argument is
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the location of the file on the machine.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</section>
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