How to override pytest logging behaviour

[mohit2152sharma]

I have created a custom logging class and I am trying to write tests for it. The class has it's own formatter, for example something like "timestamp:%(asctime)s - logger_name:%(name)s - levelname:%(levelname)s - message:%(message)s".

When i run the pytests, somehow the logs generated by this custom logger are captured in caplog with basicConfig format and on the stdout I can see the logs in the format set by custom logging class.

Following are the code snippets of how I am doing it:

# this _core.py
class CustomLogger:
    def __init__(
        self,
        name: str = "root",
        level: int = logging.INFO,
        config: Optional[dict] = None,
    ):
        self.name = name
        self.level = level

        self.config = config or CustomDefaultConf()._create_default_conf_dict()
        logging.config.dictConfig(self.config)
        logging.setLoggerClass(CustomLoggerClass)
        self.logger = logging.getLogger(name)

# in the __init__.py I expose logger
logger = CustomLogger().logger

# in the tests file
from custom_logger import logger 

def test_dummy_func(): 
    logger.info("hello world")

# in the terminal I get the following output
---------------------------------------------------------------------------------------------- Captured stdout call ----------------------------------------------------------------------------------------------
timestamp:2024-02-26 19:56:38 - logger_name:custom_logger - levelname:INFO - time_taken:1 - message:Function dummy_func took 0:00:00.000163
----------------------------------------------------------------------------------------------- Captured log call ------------------------------------------------------------------------------------------------
INFO     custom_logger.py:42 Function dummy_func took 0:00:00.000163

How can I redirect the output of my custom logger to "Captured log call"?

[portyu9]

Hi @mohit2152sharma

Those are two different handlers/output paths.

Your custom StreamHandler formats the record and writes that text to stdout, which is why you see your format under Captured stdout.

pytest's logging plugin captures the underlying LogRecord separately and formats it using pytest's own formatter, which is why Captured log call shows:

INFO custom_logger.py:42 ...

If you want pytest's captured-log section to use your format, configure pytest's log formatter:

[pytest]
log_level = INFO
log_format = timestamp:%(asctime)s - logger_name:%(name)s - levelname:%(levelname)s - message:%(message)s

You can also specify it on the command line with --log-format.

If you do not want the duplicate Captured stdout section, remove/disable the application's stdout StreamHandler for the test configuration and let the logger propagate to pytest's capture handler.

One other important detail: logging.config.dictConfig() can replace the root logger's handlers. If you configure the root logger during a test, preserve pytest's existing handlers; otherwise caplog may stop capturing altogether.

So you don't redirect the already-formatted stdout text into Captured log call; configure pytest's logging formatter to format the same LogRecord the way you want.

Please mark this answer as accepted if it helped, thank you.