How to re-run failed tests and maintain state between test runs¶
Usage¶
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
Deactivating / unregistering a plugin by name (the internal name for this plugin is
cacheprovider
).
Rerunning only failures or failures first¶
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........................ [100%]
================================= 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:7: 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:7: Failed
========================= short test summary info ==========================
FAILED test_50.py::test_num[17] - Failed: bad luck
FAILED test_50.py::test_num[25] - Failed: bad luck
2 failed, 48 passed in 0.12s
If you then run it with --lf
:
$ pytest --lf
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-8.x.y, pluggy-1.x.y
rootdir: /home/sweet/project
collected 2 items
run-last-failure: rerun previous 2 failures
test_50.py FF [100%]
================================= 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:7: 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:7: Failed
========================= short test summary info ==========================
FAILED test_50.py::test_num[17] - Failed: bad luck
FAILED test_50.py::test_num[25] - Failed: bad luck
============================ 2 failed in 0.12s =============================
You have run only the two failing tests from the last run, while the 48 passing 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-8.x.y, pluggy-1.x.y
rootdir: /home/sweet/project
collected 50 items
run-last-failure: rerun previous 2 failures first
test_50.py FF................................................ [100%]
================================= 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:7: 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:7: Failed
========================= short test summary info ==========================
FAILED test_50.py::test_num[17] - Failed: bad luck
FAILED test_50.py::test_num[25] - Failed: bad luck
======================= 2 failed, 48 passed in 0.12s =======================
New --nf
, --new-first
options: run new tests first followed by the rest
of the tests, in both cases tests are also sorted by the file modified time,
with more recent files coming first.
Behavior when no tests failed in the last run¶
The --lfnf/--last-failed-no-failures
option governs the behavior of --last-failed
.
Determines whether to execute tests when there are no previously (known)
failures or when no cached lastfailed
data was found.
There are two options:
all
: when there are no known test failures, runs all tests (the full test suite). This is the default.none
: when there are no known test failures, just emits a message stating this and exit successfully.
Example:
pytest --last-failed --last-failed-no-failures all # runs the full test suite (default behavior)
pytest --last-failed --last-failed-no-failures none # runs no tests and exits successfully
The new config.cache object¶
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 fixture which re-uses previously created state
across pytest invocations:
# content of test_caching.py
import pytest
def expensive_computation():
print("running expensive computation...")
@pytest.fixture
def mydata(pytestconfig):
val = pytestconfig.cache.get("example/value", None)
if val is None:
expensive_computation()
val = 42
pytestconfig.cache.set("example/value", val)
return val
def test_function(mydata):
assert mydata == 23
If you run this command for the first time, you can see the print statement:
$ pytest -q
F [100%]
================================= FAILURES =================================
______________________________ test_function _______________________________
mydata = 42
def test_function(mydata):
> assert mydata == 23
E assert 42 == 23
test_caching.py:19: AssertionError
-------------------------- Captured stdout setup ---------------------------
running expensive computation...
========================= short test summary info ==========================
FAILED test_caching.py::test_function - assert 42 == 23
1 failed in 0.12s
If you run it a second time, the value will be retrieved from the cache and nothing will be printed:
$ pytest -q
F [100%]
================================= FAILURES =================================
______________________________ test_function _______________________________
mydata = 42
def test_function(mydata):
> assert mydata == 23
E assert 42 == 23
test_caching.py:19: AssertionError
========================= short test summary info ==========================
FAILED test_caching.py::test_function - assert 42 == 23
1 failed in 0.12s
See the config.cache fixture
for more details.
Inspecting Cache content¶
You can always peek at the content of the cache using the
--cache-show
command line option:
$ pytest --cache-show
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-8.x.y, pluggy-1.x.y
rootdir: /home/sweet/project
cachedir: /home/sweet/project/.pytest_cache
--------------------------- cache values for '*' ---------------------------
cache/lastfailed contains:
{'test_caching.py::test_function': True}
cache/nodeids contains:
['test_caching.py::test_function']
cache/stepwise contains:
[]
example/value contains:
42
========================== no tests ran in 0.12s ===========================
--cache-show
takes an optional argument to specify a glob pattern for
filtering:
$ pytest --cache-show example/*
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-8.x.y, pluggy-1.x.y
rootdir: /home/sweet/project
cachedir: /home/sweet/project/.pytest_cache
----------------------- cache values for 'example/*' -----------------------
example/value contains:
42
========================== no tests ran in 0.12s ===========================
Clearing Cache content¶
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.
Stepwise¶
As an alternative to --lf -x
, especially for cases where you expect a large part of the test suite will fail, --sw
, --stepwise
allows you to fix them one at a time. The test suite will run until the first failure and then stop. At the next invocation, tests will continue from the last failing test and then run until the next failing test. You may use the --stepwise-skip
option to ignore one failing test and stop the test execution on the second failing test instead. This is useful if you get stuck on a failing test and just want to ignore it until later. Providing --stepwise-skip
will also enable --stepwise
implicitly.