.. versionadded:: 2.8
Warning
The functionality of this core plugin was previously distributed
as a third party plugin named pytest-cache. The core plugin
is compatible regarding command line options and API usage except that you
can only store/receive data between test runs that is json-serializable.
The plugin provides two command line options to rerun failures from the
last pytest invocation:
--lf,--last-failed- to only re-run the failures.--ff,--failed-first- to run the failures first and then the rest of the tests.
For cleanup (usually not needed), a --cache-clear option allows to remove
all cross-session cache contents ahead of a test run.
Other plugins may access the config.cache object to set/get
json encodable values between pytest invocations.
Note
This plugin is enabled by default, but can be disabled if needed: see
:ref:`cmdunregister` (the internal name for this plugin is
cacheprovider).
First, let's create 50 test invocation of which only 2 fail:
# content of test_50.py
import pytest
@pytest.mark.parametrize("i", range(50))
def test_num(i):
if i in (17, 25):
pytest.fail("bad luck")
If you run this for the first time you will see two failures:
$ pytest -q
.................F.......F........................
======= FAILURES ========
_______ test_num[17] ________
i = 17
@pytest.mark.parametrize("i", range(50))
def test_num(i):
if i in (17, 25):
> pytest.fail("bad luck")
E Failed: bad luck
test_50.py:6: Failed
_______ test_num[25] ________
i = 25
@pytest.mark.parametrize("i", range(50))
def test_num(i):
if i in (17, 25):
> pytest.fail("bad luck")
E Failed: bad luck
test_50.py:6: Failed
2 failed, 48 passed in 0.12 seconds
If you then run it with --lf:
$ pytest --lf
======= test session starts ========
platform linux -- Python 3.x.y, pytest-3.x.y, py-1.x.y, pluggy-0.x.y
run-last-failure: rerun last 2 failures
rootdir: $REGENDOC_TMPDIR, inifile:
collected 50 items
test_50.py FF
======= FAILURES ========
_______ test_num[17] ________
i = 17
@pytest.mark.parametrize("i", range(50))
def test_num(i):
if i in (17, 25):
> pytest.fail("bad luck")
E Failed: bad luck
test_50.py:6: Failed
_______ test_num[25] ________
i = 25
@pytest.mark.parametrize("i", range(50))
def test_num(i):
if i in (17, 25):
> pytest.fail("bad luck")
E Failed: bad luck
test_50.py:6: Failed
======= 48 tests deselected ========
======= 2 failed, 48 deselected in 0.12 seconds ========
You have run only the two failing test from the last run, while 48 tests have not been run ("deselected").
Now, if you run with the --ff option, all tests will be run but the first
previous failures will be executed first (as can be seen from the series
of FF and dots):
$ pytest --ff
======= test session starts ========
platform linux -- Python 3.x.y, pytest-3.x.y, py-1.x.y, pluggy-0.x.y
run-last-failure: rerun last 2 failures first
rootdir: $REGENDOC_TMPDIR, inifile:
collected 50 items
test_50.py FF................................................
======= FAILURES ========
_______ test_num[17] ________
i = 17
@pytest.mark.parametrize("i", range(50))
def test_num(i):
if i in (17, 25):
> pytest.fail("bad luck")
E Failed: bad luck
test_50.py:6: Failed
_______ test_num[25] ________
i = 25
@pytest.mark.parametrize("i", range(50))
def test_num(i):
if i in (17, 25):
> pytest.fail("bad luck")
E Failed: bad luck
test_50.py:6: Failed
======= 2 failed, 48 passed in 0.12 seconds ========
Plugins or conftest.py support code can get a cached value using the
pytest config object. Here is a basic example plugin which
implements a :ref:`fixture` which re-uses previously created state
across pytest invocations:
# content of test_caching.py
import pytest
import time
@pytest.fixture
def mydata(request):
val = request.config.cache.get("example/value", None)
if val is None:
time.sleep(9*0.6) # expensive computation :)
val = 42
request.config.cache.set("example/value", val)
return val
def test_function(mydata):
assert mydata == 23
If you run this command once, it will take a while because of the sleep:
$ pytest -q
F
======= FAILURES ========
_______ test_function ________
mydata = 42
def test_function(mydata):
> assert mydata == 23
E assert 42 == 23
test_caching.py:14: AssertionError
1 failed in 0.12 seconds
If you run it a second time the value will be retrieved from the cache and this will be quick:
$ pytest -q
F
======= FAILURES ========
_______ test_function ________
mydata = 42
def test_function(mydata):
> assert mydata == 23
E assert 42 == 23
test_caching.py:14: AssertionError
1 failed in 0.12 seconds
See the cache-api for more details.
You can always peek at the content of the cache using the
--cache-show command line option:
$ py.test --cache-show
======= test session starts ========
platform linux -- Python 3.x.y, pytest-3.x.y, py-1.x.y, pluggy-0.x.y
rootdir: $REGENDOC_TMPDIR, inifile:
cachedir: $REGENDOC_TMPDIR/.cache
------------------------------- cache values -------------------------------
cache/lastfailed contains:
{'test_caching.py::test_function': True}
example/value contains:
42
======= no tests ran in 0.12 seconds ========
You can instruct pytest to clear all cache files and values
by adding the --cache-clear option like this:
pytest --cache-clear
This is recommended for invocations from Continuous Integration servers where isolation and correctness is more important than speed.
The config.cache object allows other plugins,
including conftest.py files,
to safely and flexibly store and retrieve values across
test runs because the config object is available
in many places.
Under the hood, the cache plugin uses the simple dumps/loads API of the json stdlib module
.. currentmodule:: _pytest.cacheprovider
.. automethod:: Cache.get
.. automethod:: Cache.set
.. automethod:: Cache.makedir