PyTest Cheatsheet¶
Source¶
https://gist.github./comkwmiebach/3fd49612ef7a52b5ce3a
I have made some amendments to original version
Usage¶
(Create a symlink pytest for py.test)
Help:
pytest --help|zless
Warnings¶
There is a video I made in 'PyTest with Eric' https://www.youtube.com/watch?v=UPnXsSU9mHE which links to his article as well.
The docs also have a comprehensive set of possibilities https://docs.pytest.org/en/7.1.x/how-to/capture-warnings.html#how-to-capture-warnings.
Some options¶
-s Show Output, do not caputure
-x Stop after first failure
-k "expression" Only run tests that match expession (and fixtures)
-rs Show extra summary info for SKIPPED
-r chars Show extra test summary info as specified by chars:
(f)ailed, (E)error, (s)skipped, (x)failed, (X)passed
(w)pytest-warnings (p)passed, (P)passed with output,
(a)all except pP.
-v Verbose
-q, --quiet Less verbose
-l, --showlocals Show local variables in tracebacks
Shorter tracebacks, python tracebacks¶
pytest --tb=short
pytest --tb=line # even shorter
Use the Python standard traceback formatting:
pytest --tb=native
Output capturing¶
pytest -s # disable all capturing
https://pytest.org/latest/capture.html#capturing-of-the-stdout-stderr-output
Print a message after the test¶
The text is printed always, even in silent mode. See https://stackoverflow.com/a/38806934/362951
def report():
print("""This is printed AFTER the test""")
import atexit
atexit.register(report)
Collect information test suite / dry run¶
py.test test_sample.py --collect-only
(will not display fixture code but fixture code will be run always)
Output verbose messages¶
py.test test_sample.py -v
Run a single test: specify file.py::ClassName, like so¶
py.test -q -s test_file.py::ClassName
(fixture code will also run)
Ignore / exclude certain files or directories¶
--ignore=lib/foo/bar.py --ignore=lib/hello/
Call pytest through python¶
python -m pytest -q test_sample.py
Call pytest from python¶
Calling pytest programaticaly / from code:
import pytest
# put all arguments into a string. example:
pytest.main("g/src/app/art/__init_unit.py")
# another example:
pytest.main("-x mytestdir")
# or pass in a list of arguments:
pytest.main(['-x', 'mytestdir'])
Show available markers¶
py.test --markers
Create a reusable marker¶
content of pytest.ini:
Only run tests with names that match the "string expression"¶
py.test -k "TestClass and not test_one"
(fixture code will also run)
Only run tests that match the node ID¶
py.test test_server.py::TestClass::test_method
(fixture code will also run)
Stop after¶
py.test -x # stop after first failure
py.test --maxfail=2 # stop after two failures
py.test --maxfail=2 -rf # exit after 2 failures, report fail info.
Show local variables in tracebacks¶
py.test --showlocals
py.test -l # (shortcut)
py.test --tb=long # the default informative traceback formatting
py.test --tb=native # the Python standard library formatting
py.test --tb=short # a shorter traceback format
py.test --tb=line # only one line per failure
py.test --tb=no # no tracebak output
Drop to PDB on first failure¶
(then end test session)
py.test -x --pdb
List of the slowest 10 test durations.¶
py.test --durations=10
Send tests to multiple CPUs¶
py.test -n 4
Run tests with decorator "slowest"¶
Run tests with decorator @pytest.mark.slowest or slowest = pytest.mark.slowest; @slowest
py.test -m slowest
Show active plugins¶
Find out which plugins are active in your environment
py.test --traceconfig
Instafail¶
if pytest-instafail is installed, show errors and failures instantly instead of waiting until the end of test suite:
py.test --instafail
Expected exceptions¶
See https://pytest.org/latest/assert.html#assertions-about-expected-exceptions
Example:
def test_recursion_depth():
with pytest.raises(RuntimeError) as excinfo:
def f():
f()
f()
assert 'maximum recursion' in str(excinfo.value)
More usage examples: http://stackoverflow.com/a/15152283/362951
Excinfo is a py.code.ExceptionInfo instance: http://pylib.readthedocs.org/en/latest/code.html#py-code-exceptioninfo
Its main attributes are type (the exception class), value (the current instance), and traceback (see http://pylib.readthedocs.org/en/latest/code.html#py.code.Traceback) -
Also see https://docs.python.org/3.4/library/sys.html#sys.exc_info
Skip¶
Simple use:
Skip a whole module:Show skip reasons / info:
Advanced: https://pytest.org/latest/skipping.html
Test using parametrize¶
import pytest
@pytest.mark.parametrize(
('n', 'expected'), [
(1, 2),
(2, 3),
(3, 4),
(4, 5),
pytest.mark.xfail((1, 0)),
pytest.mark.xfail(reason="some bug")((1, 0)),
pytest.mark.skipif('sys.version_info >= (3,0)')((10, 11)),
]
)
def test_increment(n, expected):
assert n + 1 == expected
Configuration¶
See https://docs.pytest.org/en/latest/customize.html
Check if there are unexpected pytest.ini, tox.ini or setup.cfg somewhere in the project.
Known issues¶
assert error with python 3.5¶
TypeError: Call constructor takes either 0 or 3 positional arguments
Workaround: add the parameter --assert=plain to the pytest command
pytest.ini¶
Put a section marker at the top:
Line continuation¶
indent continued line by 2 spaces:*
norecursedir¶
Allows only simple directory names or patterns wihtout /, they are always applied in all subdirectories. For individual directories use: 'addopts --ignore='!
addopts¶
Example:
addopts = --ignore=./some/dir --ignore=./some/other/dir --ignore=./dir1/some.file
Helper to write dict to /tmp/data.json¶
def dump1(data, fname="/tmp/data.json"):
from json import JSONEncoder
class DateTimeAndDecimalEncoder(JSONEncoder):
def default(self, obj):
import datetime
import decimal
if isinstance(obj, datetime.datetime):
encoded_object = obj.isoformat()
# e.g. "2014-06-22T04:44:14.057000"
elif isinstance(obj, decimal.Decimal):
return str(obj)
else:
encoded_object =JSONEncoder.default(self, obj)
return encoded_object
def dumps_pretty(s):
# datetime.datetime(2013, 9, 13, 9, 59, 11) is not JSON serializable
import json
return"%s" % json.dumps(s,
sort_keys=True,
indent=2,
separators=(',', ': '),
cls=DateTimeAndDecimalEncoder,
)
f = open(fname, "w")
f.write(dumps_pretty(data))
f.close()