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I am using Python's logging module to generate an ERROR message in specific cases, followed by a sys.exit().

if platform is None:  
    logging.error(f'No platform provided!')
    sys.exit()

Continue do other stuff

Now I am using pytest to unit test the specific error message. However the sys.exit() statement causes pytest to detect an error because of a SystemExit event, even if the error message passes the test.

And mocking the sys.exit makes that the rest of the code is being run ('Continue do other stuff') which then causes other problems.

I have tried the following:

LOGGER = logging.getLogger(__name__)

platform = None
data.set_platform(platform, logging=LOGGER)
assert "No platform provided!" in caplog.text

This question is a similar: How to assert both UserWarning and SystemExit in pytest , but it raises the error in a different way.

How do I make pytest ignore the SystemExit?

laurentius
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1 Answers1

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Here is one approach.

In your test module you could write the following test, where your_module is the name of the module where your actual code is defined, and function() is the function that is doing the logging and calling sys.exit().

import logging
from unittest import mock
from your_module import function

def test_function(caplog):
    with pytest.raises(SystemExit):
        function()

    log_record = caplog.records[0]
    assert log_record.levelno == logging.ERROR
    assert log_record.message == "No platform provided!"
    assert log_record.lineno == 8   # Replace with the line no. in which log is actually called in the main code.

(If you want to shorten this a little bit, you can use record_tuples instead of records.)

EDIT: Using caplog instead of mocking the log module.

Paul P
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  • Thanks, but I don't manage to make this work. It goes wrong with the mock.patch statement: `'ModuleNotFoundError: No module named 'your_module.logging'; 'your_module' is not a package.` (In which I have replaced your_module with the name of my module). – laurentius Jun 04 '21 at 11:40
  • This is because `pytest` cannot find `your_module`. You have a couple of options on how to solve this. The simplest one is to put `your_module.py` and `test_your_module.py` (the file containing the tests) into the same directory. A few other options are outlined [here](https://stackoverflow.com/a/10253916/15282257), [here](https://stackoverflow.com/a/34140498/15282257) and [here](https://stackoverflow.com/a/50610630/15282257). – Paul P Jun 04 '21 at 11:52
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    BTW you could use the `caplog` fixture for verifying error logged instead of patching. – hoefling Jun 06 '21 at 10:01
  • Thank you, @hoefling, that's a great one! Thanks for making me aware of `caplog`! – Paul P Jun 06 '21 at 10:30