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.

Compatibility

Python xmlunittest has been tested with:

  • lxml version 3.4.0
  • 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.

Note

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!

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!

Example:

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" />
        </root>"""

        # 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 its 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.

Example:

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" />
        </root>"""

        self.assertXmlDocument(data)

Contribute

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 (in fact two, one per python version).

See an example of install (without virtualenv):

$ git clone git@github.com:YourRepo/python-xmlunittest.git xmlunittest
$ cd xmlunittest
$ pip install -r requirements.txt
$ py.test test.py
... all should be green here!

Tips

Do:

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

Don’t:

  • 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 be 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.