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It should raises an error if the

builder.build

failed

well it doesn't, you can try the following code in your python console and see:

import logging
logger = logging.getLogger(__name__)

try:
    try:
        raise ValueError()
    except Exception as e:
        logger.error("blabla, %s", e)
except:    
    print("Errored")

and see that it does not print("Errored")

builder.build call subprocess.check_output under the hood, so it should be raised

It is raised by builder.build indeed, but "logger.error" does not raise an exception so the except block silently handles the exception without raising it to the caller.