Test Tools

Python-Markdown provides some testing tools which simplify testing actual Markdown output against expected output. The tools are built on the Python standard library unittest. Therefore, no additional libraries are required. While Python-Markdown uses the tools for its own tests, they were designed and built so that third party extensions could use them as well. Therefore, the tools are importable from markdown.test_tools.

The test tools include two different unittest.TestCase subclasses: markdown.test_tools.TestCase and markdown.test_tools.LegacyTestCase.


The markdown.test_tools.TestCase class is a unittest.TestCase subclass with a few additional helpers to make testing Markdown output easier.

default_kwargs: A dict of keywords to pass to Markdown for each test. The defaults can be overridden on individual tests.
assertMarkdownRenders: accepts the source text, the expected output, an optional dictionary of expected_attrs, and any keywords to pass to Markdown. The default_kwargs defined on the class are used except where overridden by keyword arguments. The output and expected output are passed to TestCase.assertMultiLineEqual. An AssertionError is raised with a diff if the actual output does not equal the expected output. The optional keyword expected_attrs accepts a dictionary of attribute names as keys with expected values. Each value is checked against the attribute of that name on the instance of the Markdown class using TestCase.assertEqual. An AssertionError is raised if any value does not match the expected value.
dedent: Dedent triple-quoted strings.

In all other respects, markdown.test_tools.TestCase behaves as unittest.TestCase. In fact, assertMarkdownRenders tests could be mixed with other unittest style tests within the same test class.

An example Markdown test might look like this:

from markdown.test_tools import TestCase

class TestHr(TestCase):
    def test_hr_before_paragraph(self):
            # The Markdown source text used as input
                An HR followed by a paragraph with no blank line.
            # The expected HTML output
                <p>An HR followed by a paragraph with no blank line.</p>
            # Other keyword arguments to pass to `markdown.markdown`


In the past Python-Markdown exclusively used file-based tests. Many of those tests still exist in Python-Markdown’s test suite, including the test files from the reference implementation (markdown.pl) and PHP Markdown. Each test consists of a matching pair of text and HTML files. The text file contains a snippet of Markdown source text formatted for a specific syntax feature and the HTML file contains the expected HTML output of that snippet. When the test suite is run, each text file is run through Markdown and the output is compared with the HTML file as a separate unit test. When a test fails, the error report includes a diff of the expected output compared to the actual output to easily identify any problems.

A separate markdown.test_tools.LegacyTestCase subclass must be created for each directory of test files. Various properties can be defined within the subclass to point to a directory of text-based test files and define various behaviors/defaults for those tests. The following properties are supported:

  • location: A path to the directory of test files. An absolute path is preferred.
  • exclude: A list of tests to skip. Each test name should comprise of a file name without an extension.
  • normalize: A boolean value indicating if the HTML should be normalized. Default: False. Note: Normalization of HTML requires that PyTidyLib be installed on the system. If PyTidyLib is not installed and normalize is set to True, then the test will be skipped, regardless of any other settings.
  • input_ext: A string containing the file extension of input files. Default: .txt.
  • output_ext: A string containing the file extension of expected output files. Default: html.
  • default_kwargs: A markdown.test_tools.Kwargs instance which stores the default set of keyword arguments for all test files in the directory.

In addition, properties can be defined for each individual set of test files within the directory. The property should be given the name of the file without the file extension. Any spaces and dashes in the file name should be replaced with underscores. The value of the property should be a markdown.test_tools.Kwargs instance which contains the keyword arguments that should be passed to markdown.markdown for that test file. The keyword arguments will “update” the default_kwargs.

When the class instance is created during a test run, it will walk the given directory and create a separate unit test for each set of test files using the naming scheme: test_filename. One unit test will be run for each set of input and output files.

The definition of an example set of tests might look like this:

from markdown.test_tools import LegacyTestCase, Kwargs
import os

# Get location of this file and use to find text file dirs.
parent_test_dir = os.path.abspath(os.path.dirname(__file__))

class TestFoo(LegacyTestCase):
    # Define location of text file directory. In this case, the directory is
    # named "foo" and is in the same parent directory as this file.
    location = os.path.join(parent_test_dir, 'foo')
    # Define default keyword arguments. In this case, unless specified
    # differently, all tests should use the output format "html".
    default_kwargs = Kwargs(output_format='html')

    # The "xhtml" test should override the output format and use "xhtml".
    xhtml = Kwargs(output_format='xhtml')

    # The "toc" test should use the "toc" extension with a custom permalink
    # setting.
    toc = Kwargs(
        extension_configs={'markdown.extensions.toc': {'permalink': "[link]"}}

Note that in the above example, the text file directory may contain many more text-based test files than xhtml (xhtml.txt and xhtml.html) and toc (toc.txt and toc.html). As long as each set of files exists as a pair, a test will be created and run for each of them. Only the xhtml and toc tests needed to be specifically identified as they had specific, non-default settings which needed to be defined.

Running Python-Markdown’s Tests

As all of the tests for the markdown library are unit tests, standard unittest methods of calling tests can be used. For example, to run all of Python-Markdown’s tests, from the root of the git repository, run the following command:

python -m unittest discover tests

That simple command will search everything in the tests directory and it’s sub-directories and run all unittest tests that it finds, including unittest.TestCase, markdown.test_tools.TestCase, and markdown.test_tools.LegacyTestCase subclasses. Normal unittest discovery rules apply.

See Also

See the Contributing Guide for instructions on setting up a development environment for running the tests.