How to run doctests¶
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:
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 =========================== test session starts ============================ platform linux -- Python 3.x.y, pytest-7.x.y, pluggy-1.x.y rootdir: /home/sweet/project collected 1 item test_example.txt . [100%] ============================ 1 passed in 0.12s =============================
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-7.x.y, pluggy-1.x.y rootdir: /home/sweet/project collected 2 items mymodule.py . [ 50%] test_example.txt . [100%] ============================ 2 passed in 0.12s =============================
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
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¶
doctest module provides some options
to configure the strictness of doctest tests. In pytest, you can enable those flags using the
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
uprefix 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
bprefix 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. The numbers are compared using
pytest.approx()with relative tolerance equal to the precision. For example, the following output would only need to match to 2 decimal places when comparing
>>> math.pi 3.14
If you wrote
3.1416then the actual output would need to match to approximately 4 decimal places; and so on.
This avoids false positives caused by limited floating-point precision, like this:
Expected: 0.233 Got: 0.23300000000000001
NUMBERalso 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_optionflagsin your configuration file.
New in version 5.1.
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
You can change the diff output format on failure for your doctests
by using one of standard doctest modules format in options
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
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
It is possible to use fixtures using the
# content of example.rst >>> tmp = getfixture('tmp_path') >>> ... >>>
Note that the fixture needs to be defined in a place visible by pytest, for example, a
file or plugin; normal python files containing docstrings are not normally scanned for fixtures
unless explicitly configured by
Also, the usefixtures mark and fixtures marked as autouse are supported when executing text doctest files.
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 """
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!
For the same reasons one might want to skip normal tests, it is also possible to skip tests inside doctests.
To skip a single check inside a doctest you can use the standard
def test_random(y): """ >>> random.random() # doctest: +SKIP 0.156231223 >>> 1 + 1 2 """
This will skip the first check, but not the second.
pytest also allows using the standard pytest functions
pytest.xfail() inside doctests, which might be useful because you can
then skip/xfail tests based on external conditions:
>>> import sys, pytest >>> if sys.platform.startswith('win'): ... pytest.skip('this doctest does not work on Windows') ... >>> import fcntl >>> ...
However using those functions is discouraged because it reduces the readability of the docstring.
pytest.xfail() behave differently depending
if the doctests are in a Python file (in docstrings) or a text file containing
doctests intermingled with text:
Python modules (docstrings): the functions only act in that specific docstring, letting the other docstrings in the same module execute as normal.
Text files: the functions will skip/xfail the checks for the rest of the entire file.
While the built-in pytest support provides a good set of functionalities for using doctests, if you use them extensively you might be interested in those external packages which add many more features, and include pytest integration:
pytest-doctestplus: provides advanced doctest support and enables the testing of reStructuredText (“.rst”) files.
Sybil: provides a way to test examples in your documentation by parsing them from the documentation source and evaluating the parsed examples as part of your normal test run.