Doctest integration for modules and test files

By default all files matching the test*.txt pattern will be run through the python standard doctest module. You can change the pattern by issuing:

pytest --doctest-glob='*.rst'

on the command line. --doctest-glob can be given multiple times in the command-line.

If you then have a text file like this:

# content of test_example.txt

hello this is a doctest
>>> x = 3
>>> x
3

then you can just invoke pytest directly:

$ pytest
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-5.x.y, py-1.x.y, pluggy-0.x.y
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collected 1 item

test_example.txt .                                                   [100%]

============================ 1 passed in 0.01s =============================

By default, pytest will collect test*.txt files looking for doctest directives, but you can pass additional globs using the --doctest-glob option (multi-allowed).

In addition to text files, you can also execute doctests directly from docstrings of your classes and functions, including from test modules:

# content of mymodule.py
def something():
    """ a doctest in a docstring
    >>> something()
    42
    """
    return 42
$ pytest --doctest-modules
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-5.x.y, py-1.x.y, pluggy-0.x.y
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collected 2 items

mymodule.py .                                                        [ 50%]
test_example.txt .                                                   [100%]

============================ 2 passed in 0.01s =============================

You can make these changes permanent in your project by putting them into a pytest.ini file like this:

# content of pytest.ini
[pytest]
addopts = --doctest-modules

Note

The builtin pytest doctest supports only doctest blocks, but if you are looking for more advanced checking over all your documentation, including doctests, .. codeblock:: python Sphinx directive support, and any other examples your documentation may include, you may wish to consider Sybil. It provides pytest integration out of the box.

Encoding

The default encoding is UTF-8, but you can specify the encoding that will be used for those doctest files using the doctest_encoding ini option:

# content of pytest.ini
[pytest]
doctest_encoding = latin1

Using ‘doctest’ options

Python’s standard doctest module provides some options to configure the strictness of doctest tests. In pytest, you can enable those flags using the configuration file.

For example, to make pytest ignore trailing whitespaces and ignore lengthy exception stack traces you can just write:

[pytest]
doctest_optionflags= NORMALIZE_WHITESPACE IGNORE_EXCEPTION_DETAIL

Alternatively, options can be enabled by an inline comment in the doc test itself:

>>> something_that_raises()  # doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
ValueError: ...

pytest also introduces new options:

  • ALLOW_UNICODE: when enabled, the u prefix is stripped from unicode strings in expected doctest output. This allows doctests to run in Python 2 and Python 3 unchanged.

  • ALLOW_BYTES: similarly, the b prefix is stripped from byte strings in expected doctest output.

  • NUMBER: when enabled, floating-point numbers only need to match as far as the precision you have written in the expected doctest output. For example, the following output would only need to match to 2 decimal places:

    >>> math.pi
    3.14
    

    If you wrote 3.1416 then the actual output would need to match to 4 decimal places; and so on.

    This avoids false positives caused by limited floating-point precision, like this:

    Expected:
        0.233
    Got:
        0.23300000000000001
    

    NUMBER also supports lists of floating-point numbers – in fact, it matches floating-point numbers appearing anywhere in the output, even inside a string! This means that it may not be appropriate to enable globally in doctest_optionflags in your configuration file.

Continue on failure

By default, pytest would report only the first failure for a given doctest. If you want to continue the test even when you have failures, do:

pytest --doctest-modules --doctest-continue-on-failure

Output format

You can change the diff output format on failure for your doctests by using one of standard doctest modules format in options (see doctest.REPORT_UDIFF, doctest.REPORT_CDIFF, doctest.REPORT_NDIFF, doctest.REPORT_ONLY_FIRST_FAILURE):

pytest --doctest-modules --doctest-report none
pytest --doctest-modules --doctest-report udiff
pytest --doctest-modules --doctest-report cdiff
pytest --doctest-modules --doctest-report ndiff
pytest --doctest-modules --doctest-report only_first_failure

pytest-specific features

Some features are provided to make writing doctests easier or with better integration with your existing test suite. Keep in mind however that by using those features you will make your doctests incompatible with the standard doctests module.

Using fixtures

It is possible to use fixtures using the getfixture helper:

# content of example.rst
>>> tmp = getfixture('tmpdir')
>>> ...
>>>

Also, Using fixtures from classes, modules or projects and Autouse fixtures (xUnit setup on steroids) fixtures are supported when executing text doctest files.

‘doctest_namespace’ fixture

The doctest_namespace fixture can be used to inject items into the namespace in which your doctests run. It is intended to be used within your own fixtures to provide the tests that use them with context.

doctest_namespace is a standard dict object into which you place the objects you want to appear in the doctest namespace:

# content of conftest.py
import numpy


@pytest.fixture(autouse=True)
def add_np(doctest_namespace):
    doctest_namespace["np"] = numpy

which can then be used in your doctests directly:

# content of numpy.py
def arange():
    """
    >>> a = np.arange(10)
    >>> len(a)
    10
    """
    pass

Note that like the normal conftest.py, the fixtures are discovered in the directory tree conftest is in. Meaning that if you put your doctest with your source code, the relevant conftest.py needs to be in the same directory tree. Fixtures will not be discovered in a sibling directory tree!

Skipping tests dynamically

New in version 4.4.

You can use pytest.skip to dynamically skip doctests. For example:

>>> import sys, pytest
>>> if sys.platform.startswith('win'):
...     pytest.skip('this doctest does not work on Windows')
...