Python XML-Unittest

Anyone uses XML, for RSS, for configuration files, for... well, we all use XML for our own reasons (folk says one can not simply uses XML, but still...).

So, your code generates XML, and everything is fine. As you follow best practices (if you don’t, I think you should), you have written some good unit-tests, where you compare code’s result with an expected result. I mean you compare string with string. Do you see the issue here? If you don’t, well, good for you. I see a lot of issue with this approach.

XML is not a simple string, it is a structured document. One can not simply compare two XML string and expect all being fine: attributes’s order can change unexpectedly, elements can be optional, and no one can explain simply how spaces and tabs works in XML formatting.

Here comes XML unittest TestCase: if you want to use the built-in unittest package (or if it is a requirement), and you are not afraid of using xpath expression with lxml, this library is made for you.

You will be able to test your XML document, and use the power of xpath and various schema languages to write tests that matter.


Python xmlunittest has been tested with:

  • lxml version 3.0 and 3.4.
  • Python 2.7.6
  • Python 3.4.0

Be aware: as a lot of string manipulation is involved, a lot of issues can happen with unicode/bytestring. It’s always a bit tough when dealing with a Py2/Py3 compatible library.


Python 2.7.6 support is maintained for now, but it will be eventually dropped. It’s never too late to switch to Python 3!

LXML version 2.x or 3.x?

When dealing with version number, it appears that xmlunittest works with:

  • Python 2.7 and lxml 2.3.5 and above.
  • Pytonn 3.4 and lmxl 3.0 and above.


No, xmlunittest does not work with Python 3 and an older version of lxml < 3.0. Also, note that this package is only tested with lxml >= 3.0. It works, but without warranty.

Why not Python 3.3?

This package works with Python 2.7, but it’s only because we are lucky enough. This is a small project, and it does not aim to support more than one major version of python. The latest, the better!

How to

  • Extends xmlunittest.XmlTestCase
  • Write your tests, using the function or method that generate XML document
  • Use xmlunittest.XmlTestCase‘s assertion methods to validate
  • Keep your test readable!


from xmlunittest import XmlTestCase

class CustomTestCase(XmlTestCase):

    def test_my_custom_test(self):
        # In a real case, data come from a call to your function/method.
        data = """<?xml version="1.0" encoding="UTF-8" ?>
        <root xmlns:ns="uri">
            <leaf id="1" active="on" />
            <leaf id="2" active="on" />
            <leaf id="3" active="off" />

        # Everything starts with `assertXmlDocument`
        root = self.assertXmlDocument(data)

        # Check namespace
        self.assertXmlNamespace(root, 'ns', 'uri')

        # Check
        self.assertXpathsUniqueValue(root, ('./leaf@id', ))
        self.assertXpathValues(root, './leaf@active', ('on', 'off'))

Alternativly, one can use the XmlTestMixin instead of the XmlTestCase, as long as their own class also extends unittest.TestCase.

This is convenient when there is already a subclass of unittest.TestCase and one also wants to profit of XML assertions.


import unittest

from xmlunittest import XmlTestMixin

class CustomTestCase(unittest.TestCase, XmlTestMixin):

    def test_my_custom_test(self):
        # write exactly the same test as in previous example

        data = """<?xml version="1.0" encoding="UTF-8" ?>
        <root xmlns:ns="uri">
            <leaf id="1" active="on" />
            <leaf id="2" active="on" />
            <leaf id="3" active="off" />



First of all, thanks for reading this!

You use xmlunittest and you have to write the same utility method again and again? If it is related only to XML tests, maybe you can share it?

Good! How can you do that?

First, you can fork the project’s github repository, then you will need some tools for development: all dependencies are available into the requirements.txt file. You should also use a virtualenv (use two for each version, or use tox).

See an example of install (without virtualenv):

$ git clone xmlunittest
$ cd xmlunittest
$ pip install -r requirements.txt
$ py.test
... all should be green here!


Installing lxml is not easy if you are not prepared. You will need some extra source package on your favorite OS (in particular some XML libs and python sources).

Testing with tox

Now that xmlunittest uses tox to run the tests, it’s even easier to perform tests on multiple version of python. Instead of using py.test do:

$ tox test

And that’s all! Remember: Python 2.7 and Python 3.4. Nothing more.



  • Always test with both Python 2.7 and Python 3.4 - use Tox!
  • Always test with namespaces
  • Always provide unit-tests.
  • Always provide documentation.
  • It’s better to respect PEP8.


  • Never add any other library. xmlunittest uses lxml and that’s enough!
  • If you have to add a data.encode(charset) into an assert method, it’s probably not a good idea.
  • XML documents can not be compared as simple strings. Don’t compare them as simple string. Don’t.
  • Don’t write more than 80 characters per line. Please. Don’t.