* Stuff for automatic and manual testing of NixOS VMs.

  lib/build-vms.nix contains a function `buildVirtualNetwork' that
  takes a specification of a network of machines (as an attribute set
  of NixOS machine configurations) and builds a script that starts
  each configuration in a separate QEMU/KVM VM and connects them
  together in a virtual network.  This script can be run manually to
  test the VMs interactively.  There is also a function `runTests'
  that starts and runs the virtual network in a derivation, and
  then executes a test specification that tells the VMs to do certain
  things (i.e., letting one VM send an HTTP request to a webserver on
  another VM).  The tests are written in Perl (for now).

  tests/subversion.nix shows a simple example, namely a network of two
  machines: a webserver that runs the Subversion subservice, and a
  client.  Apache, Subversion and a few other packages are built with
  coverage analysis instrumentation.  For instance,

    $ nix-build tests/subversion.nix -A vms
    $ ./result/bin/run-vms

  starts two QEMU/KVM instances.  When they have finished booting, the
  webserver can be accessed from the host through
  http://localhost:8081/.

  It also has a small test suite:

    $ nix-build tests/subversion.nix -A report

  This runs the VMs in a derivation, runs the tests, and then produces
  a distributed code coverage analysis report (i.e. it shows the
  combined coverage on both machines).

  The Perl test driver program is in lib/test-driver.  It executes
  commands on the guest machines by connecting to a root shell running
  on port 514 (provided by modules/testing/test-instrumentation.nix).

  The VMs are connected together in a virtual network using QEMU's
  multicast feature.  This isn't very secure.  At the very least,
  other processes on the same machine can listen to or send packets on
  the virtual network.  On the plus side, we don't need to be root to
  set up a multicast virtual network, so we can do it from a
  derivation.  Maybe we can use VDE instead.

  (Moved from the vario repository.)

svn path=/nixos/trunk/; revision=16899