Testing XML with rspec, xpath and libxml

I’m currently working with the virtualization API libvirt which uses XML to represent virtual machines and I’m generating this XML using Ruby.  I’m using rspec to test my code and wanted to test that my output was as I expected.  I started out with rspec-hpricot-matchers which worked fine until I started testing slightly more complex xml, which hpricot wasn’t handling well.

So I wrote a have_xml matcher using the rspec dsl which uses the libxml library to do the testing.  It’s so simple it’s not really worthy of a gem, so here it is (licensed under public domain).  The text check is optional and, to be honest, doesn’t belong here really.  It should be a separate matcher.

require 'libxml'

Spec::Matchers.define :have_xml do |xpath, text|
  match do |body|
    parser = LibXML::XML::Parser.string body
    doc = parser.parse
    nodes = doc.find(xpath)
    nodes.empty?.should be_false
    if text
      nodes.each do |node|
        node.content.should == text

  failure_message_for_should do |body|
    "expected to find xml tag #{xpath} in:\n#{body}"

  failure_message_for_should_not do |response|
    "expected not to find xml tag #{xpath} in:\n#{body}"

  description do
    "have xml tag #{xpath}"

So, add that somewhere (usually spec/spec_helper.rb) and use it like this:

it "should include the xen_machine_id" do
  @xml.should have_xml('/domain/name', 'bb-example-001')

it "should include the network devices" do
  @xml.should have_xml "/domain/devices/interface[1]/ip[@address='']"
  @xml.should have_xml "/domain/devices/interface[1]/mac[@address='aa:00:01:02:03:04']"
  @xml.should have_xml "/domain/devices/interface[1]/script[@path='/etc/xen/scripts/vif-bridge']"
  @xml.should have_xml "/domain/devices/interface[1]/source[@bridge='inetbr']"


DaveK says:

You mean you’ve been spending all this time doing XML when you could have been doing ELER? Shame on you, shame!

Chris says:

Great. Thanks John.

Alex says:

Awesome! Thank you!

Faun says:

I have updated this matcher to use Rspec 2 syntax and Nokogiri.
See https://gist.github.com/4279964

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