virt-v2v-test-harness man page

virt-v2v-test-harness — Used to test virt-v2v against real test cases


 open V2v_test_harness
 let test = "rhel_45_i386_fv"
 let test_plan = {
   default_plan with
     boot_plan = Boot_to_screenshot (test ^ "-login.ppm")
 let () = run ~test ~test_plan ()


virt-v2v(1) converts guests from a foreign hypervisor to run on KVM, managed by libvirt, OpenStack, oVirt, Red Hat Virtualisation (RHV) or several other targets.

Virt-v2v-test-harness is a small library (module name: V2v_test_harness) used to run virt-v2v against a set of test cases consisting of real virtual machines.

It acts as a test harness, taking a test case, running virt-v2v on it (non-destructively), then test-booting the result.  It can ensure that the test case converts successfully, boots successfully, and reaches a milestone (such as a particular screenshot).  It can also test that the conversion created, modified or deleted the expected files from within the guest.

Getting the Test Cases

Because the test cases are actual virtual machines, we split them into two groups: test cases which are freely redistributable and those which are proprietary.  The former are things like Fedora or CentOS images, which are free software.  The latter are things like Windows or Red Hat Enterprise Linux.

The freely redistributable test cases can be downloaded from: not available yet

The proprietary test cases are available at This does not contain the proprietary images themselves, which are not made available to the public for licensing reasons.

The test cases consist of disk images which are very large, from 250 MB through to tens of gigabytes each.  This means that distributing test cases can be very time-consuming and expensive.  We use git-annex(1) to distribute the test images.


It’s recommended to use an idle machine for testing.  You will need a lot of disk space to run the tests, in excess of 100 GB.  You should also ensure the test machine has plenty of RAM, at least 16 GB.

Getting the Test Harness

To run the test cases you must have the virt-v2v test harness.

The OCaml module is V2v_test_harness.

The easiest way is to compile libguestfs from source (note do not install it).  The test harness will be in virt-v2v.git/test-harness

It is also possible to install test harness as an OCaml module.

Running the Test Cases

Once you have checked out the freely redistributed test cases from the repository, do:

 ./configure [--with-test-harness=/path/to/virt-v2v/test-harness]
 make check -k

Using the -k option is recommended so the test doesn't stop at the first failure.

Parallel Tests

You can run test cases in parallel by doing:

 make check -k -j<N>

(eg. -j2 for running up to 2 tests in parallel).  Be careful about running too many parallel tests, as it can slow down each test enough to cause false failures.

Running Test Cases Against Upstream Virt-V2v

Using make check picks up whatever virt-v2v binary is on your $PATH.

If you have compiled libguestfs from source and want to test that version of virt-v2v, use the libguestfs run script (in the top-level build directory of the libguestfs sources).  eg:

 ../libguestfs/run make check -k

Writing New Test Cases

If you are interested in writing test cases, it is suggested that you start by downloading the freely redistributable test cases, or at least look at them online.

Also you must have the virt-v2v test harness - see “Getting the Test Harness” above.

Files in Each Test Case

Each test case consists of:


The disk image of the virtual machine before conversion.  Usually this should be converted to raw format and xz-compressed.


Alternatively, an OVA, exported from VMware, may be used.


The libvirt XML used as input to virt-v2v.  See the discussion of -i libvirtxml in virt-v2v(1).


An optional screenshot or screenshots.

You can supply zero or more “known good” screenshots which represent intermediate steps where the guest is booting.  This is useful where a guest sits for some time doing something, and lets the test harness know that it should allow the guest to continue to boot.

You can supply zero or one “final” screenshot.  This is often a screenshot of the login page which indicates that the guest booted successfully.

The screenshots are captured using virsh(1).  Comparison of screenshots against the test images is done using the ImageMagick compare(1) program.

The test itself - see below.

Writing the Test

The test file (*.ml) is used to control the test harness, and minimally it would look something like this:

 open V2v_test_harness
 let test = "short_name"
 let () = run ~test ()

That would instruct the test harness to:

  • Uncompress short_name.img.xz
  • Run virt-v2v -i libvirtxml short_name.xml [...]
  • Boot the resulting guest and check that it writes to its disk and then the disk becomes idle.

The above is a rather simplistic test.  A more realistic test is to ensure the guest reaches a final milestone (screenshot), eg. a login page.  To do that you have to supply a ~test_plan parameter:

 open V2v_test_harness
 let test = "short_name"
 let test_plan = {
   default_plan with
     boot_plan = Boot_to_screenshot (test ^ ".ppm")
 let () = run ~test ~test_plan ()

For an even better test, you can supply post-conversion and post-boot test cases which examine the disk image (using libguestfs) to verify that files have been created, modified or deleted as expected within the disk image.  See V2v_test_harness.mli for more information on how to do that.

Files Generated by Running the Test

When you run each test, the following files can be created:


Screenshot(s) of the guest’s graphical console.  These are helpful when writing tests or debugging test failures.

The screenshot format is Portable Pixmap (PPM).


The uncompressed original disk image (before conversion).


The result of conversion, ie. after running virt-v2v but before test-booting the guest.  See the virt-v2v(1) manual page description of -o local.

The disk image format is qcow2.


The disk image after test-booting.  This is a qcow2 file which uses the test-converted-sda file as a backing disk, in order to save disk space.



The test library interface.  Read this for detailed programming documentation.


The findlib META file allowing you to use the library from ocamlfind(1).

NB: To find the value of $ocamllibdir, run ocamlc -where

See Also

virt-v2v(1), virt-p2v(1), guestfs(3), virsh(1), compare(1), git-annex(1),


Richard W.M. Jones


This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA


To get a list of bugs against libguestfs, use this link:

To report a new bug against libguestfs, use this link:

When reporting a bug, please supply:

Referenced By

guestfs-release-notes-1.30(1), virt-v2v(1).

2019-11-18 virt-v2v-1.41.8 Virtualization Support