I'm trying to use TDD (test-driven development) with pytest
.
pytest
will not print
to the console when I use print
.
I am using pytest my_tests.py
to run it.
The documentation
seems to say that it should work by default: http://pytest.org/latest/capture.html
But:
import myapplication as tum
class TestBlogger:
@classmethod
def setup_class(self):
self.user = "alice"
self.b = tum.Blogger(self.user)
print "This should be printed, but it won't be!"
def test_inherit(self):
assert issubclass(tum.Blogger, tum.Site)
links = self.b.get_links(posts)
print len(links) # This won't print either.
Nothing gets printed to my standard output console (just the normal progress and how many many tests passed/failed).
And the script that I'm testing contains print:
class Blogger(Site):
get_links(self, posts):
print len(posts) # It won't get printed in the test.
In unittest
module, everything gets printed by default, which is exactly what I need. However, I wish to use pytest
for other reasons.
Does anyone know how to make the print statements get shown?
This question is related to
python
unit-testing
python-2.7
pytest
I originally came in here to find how to make PyTest
print in VSCode's console while running/debugging the unit test from there. This can be done with the following launch.json
configuration. Given .venv
the virtual environment folder.
"version": "0.2.0",
"configurations": [
{
"name": "PyTest",
"type": "python",
"request": "launch",
"stopOnEntry": false,
"pythonPath": "${config:python.pythonPath}",
"module": "pytest",
"args": [
"-sv"
],
"cwd": "${workspaceRoot}",
"env": {},
"envFile": "${workspaceRoot}/.venv",
"debugOptions": [
"WaitOnAbnormalExit",
"WaitOnNormalExit",
"RedirectOutput"
]
}
]
}
According to the pytest docs, pytest --capture=sys
should work. If you want to capture standard out inside a test, refer to the capsys fixture.
I needed to print important warning about skipped tests exactly when PyTest
muted literally everything.
I didn't want to fail a test to send a signal, so I did a hack as follow:
def test_2_YellAboutBrokenAndMutedTests():
import atexit
def report():
print C_patch.tidy_text("""
In silent mode PyTest breaks low level stream structure I work with, so
I cannot test if my functionality work fine. I skipped corresponding tests.
Run `py.test -s` to make sure everything is tested.""")
if sys.stdout != sys.__stdout__:
atexit.register(report)
The atexit
module allows me to print stuff after PyTest
released the output streams. The output looks as follow:
============================= test session starts ==============================
platform linux2 -- Python 2.7.3, pytest-2.9.2, py-1.4.31, pluggy-0.3.1
rootdir: /media/Storage/henaro/smyth/Alchemist2-git/sources/C_patch, inifile:
collected 15 items
test_C_patch.py .....ssss....s.
===================== 10 passed, 5 skipped in 0.15 seconds =====================
In silent mode PyTest breaks low level stream structure I work with, so
I cannot test if my functionality work fine. I skipped corresponding tests.
Run `py.test -s` to make sure everything is tested.
~/.../sources/C_patch$
Message is printed even when PyTest
is in silent mode, and is not printed if you run stuff with py.test -s
, so everything is tested nicely already.
Use the -s
option:
pytest -s
From the docs:
During test execution any output sent to stdout and stderr is captured. If a test or a setup method fails its according captured output will usually be shown along with the failure traceback.
pytest
has the option --capture=method
in which method
is per-test capturing method, and could be one of the following: fd
, sys
or no
. pytest
also has the option -s
which is a shortcut for --capture=no
, and this is the option that will allow you to see your print statements in the console.
pytest --capture=no # show print statements in console
pytest -s # equivalent to previous command
There are two ways in which pytest
can perform capturing:
file descriptor (FD) level capturing (default): All writes going to the operating system file descriptors 1 and 2 will be captured.
sys level capturing: Only writes to Python files sys.stdout and sys.stderr will be captured. No capturing of writes to filedescriptors is performed.
pytest -s # disable all capturing
pytest --capture=sys # replace sys.stdout/stderr with in-mem files
pytest --capture=fd # also point filedescriptors 1 and 2 to temp file
Using -s
option will print output of all functions, which may be too much.
If you need particular output, the doc page you mentioned offers few suggestions:
Insert assert False, "dumb assert to make PyTest print my stuff"
at the end of your function, and you will see your output due to failed test.
You have special object passed to you by PyTest, and you can write the output into a file to inspect it later, like
def test_good1(capsys):
for i in range(5):
print i
out, err = capsys.readouterr()
open("err.txt", "w").write(err)
open("out.txt", "w").write(out)
You can open the out
and err
files in a separate tab and let editor automatically refresh it for you, or do a simple py.test; cat out.txt
shell command to run your test.
That is rather hackish way to do stuff, but may be it is the stuff you need: after all, TDD means you mess with stuff and leave it clean and silent when it's ready :-).
Source: Stackoverflow.com