chromium/src/third_party/blink/tools/blinkpy/common/system/log_testing.py

# Copyright (C) 2010 Chris Jerdonek (cjerdonek@webkit.org)
#
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# 1.  Redistributions of source code must retain the above copyright
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"""Supports the unit-testing of logging code.

Provides support for unit-testing messages logged using the built-in
logging module.

Inherit from the LoggingTestCase class for basic testing needs.  For
more advanced needs (e.g. unit-testing methods that configure logging),
see the TestLogStream class, and perhaps also the LogTesting class.
"""

import logging
import unittest

# pylint: disable=invalid-name
# Camel-case names were used here to match the style of the TestCase
# methods. It would also be alright to change these to lowercase.


class TestLogStream(object):
    """Represents a file-like object for unit-testing logging.

    This is meant for passing to the logging.StreamHandler constructor.
    Log messages captured by instances of this object can be tested
    using self.assertMessages() below.
    """

    def __init__(self, test_case):
        """Creates an instance.

        Args:
            test_case: A unittest.TestCase instance.
        """
        self._test_case = test_case
        self.messages = []  # A list of log messages written to the stream.

    # Python documentation says that any object passed to the StreamHandler
    # constructor should support write() and flush().
    #
    # http://docs.python.org/library/logging.html#module-logging.handlers

    def write(self, message):
        self.messages.append(message)

    def flush(self):
        pass

    def assertMessages(self, messages):
        """Asserts that the given messages match the logged messages."""
        self._test_case.assertEqual(messages, self.messages)


class LogTesting(object):
    """Supports end-to-end unit-testing of log messages.

    Sample usage:

      class SampleTest(unittest.TestCase):

          def setUp(self):
              self._log = LogTesting.setUp(self)  # Turn logging on.

          def tearDown(self):
              self._log.tearDown()  # Turn off and reset logging.

          def test_logging_in_some_method(self):
              call_some_method()  # Contains calls to _log.info(), etc.

              # Check the resulting log messages.
              self._log.assertMessages(["INFO: expected message #1",
                                      "WARNING: expected message #2"])
    """

    def __init__(self, test_stream, handler):
        """Creates an instance.

        This method should never be called directly. Instances should
        instead be created using the static setUp() method.

        Args:
            test_stream: A TestLogStream instance.
            handler: The handler added to the logger.
        """
        self._test_stream = test_stream
        self._handler = handler

    @staticmethod
    def _getLogger():
        """Returns the logger being tested."""
        # It is possible we might want to return something other than
        # the root logger in some special situation.  For now, the
        # root logger seems to suffice.
        return logging.getLogger()

    @staticmethod
    def setUp(test_case, logging_level=logging.INFO):
        """Configures logging for unit testing.

        Configures the root logger to log to a testing log stream.
        Only messages logged at or above the given level are logged
        to the stream.  Messages logged to the stream are formatted
        in the following way, for example--

        "INFO: This is a test log message."

        This method should normally be called in the setUp() method
        of a unittest.TestCase.  See the docstring of this class
        for more details.

        Args:
            test_case: A unittest.TestCase instance.
            logging_level: An integer logging level that is the minimum level
                           of log messages you would like to test.

        Returns:
            A LogTesting instance.
        """
        stream = TestLogStream(test_case)
        handler = logging.StreamHandler(stream)
        handler.setLevel(logging_level)
        formatter = logging.Formatter('%(levelname)s: %(message)s')
        handler.setFormatter(formatter)

        # Notice that we only change the root logger by adding a handler
        # to it.  In particular, we do not reset its level using
        # logger.setLevel().  This ensures that we have not interfered
        # with how the code being tested may have configured the root
        # logger.
        logger = LogTesting._getLogger()
        logger.setLevel(logging_level)
        logger.addHandler(handler)

        return LogTesting(stream, handler)

    def tearDown(self):
        """Resets logging."""
        logger = LogTesting._getLogger()
        logger.removeHandler(self._handler)

    def messages(self):
        """Returns the current list of log messages."""
        return self._test_stream.messages

    def assertMessages(self, messages):
        """Asserts the current array of log messages, and clear its contents.

        We clear the log messages after asserting since they are no longer
        needed after asserting.  This serves two purposes: (1) it simplifies
        the calling code when we want to check multiple logging calls in a
        single test method, and (2) it lets us check in the tearDown() method
        that there are no remaining log messages to be asserted.

        The latter ensures that no extra log messages are getting logged that
        the caller might not be aware of or may have forgotten to check for.
        This gets us a bit more mileage out of our tests without writing any
        additional code.

        We want to clear the array of messages even in the case of
        an Exception (e.g. an AssertionError).  Otherwise, another
        AssertionError can occur in the tearDown() because the
        array might not have gotten emptied.

        Args:
            messages: A list of log message strings.
        """
        try:
            self._test_stream.assertMessages(messages)
        finally:
            self._test_stream.messages = []


class LoggingTestCase(unittest.TestCase):
    """Supports end-to-end unit-testing of log messages.

    This class needs to inherit from unittest.TestCase.  Otherwise, the
    setUp() and tearDown() methods will not get fired for test case classes
    that inherit from this class -- even if the class inherits from *both*
    unittest.TestCase and LoggingTestCase.

    Sample usage:

      class SampleTest(LoggingTestCase):

          def test_logging_in_some_method(self):
              call_some_method()  # Contains calls to _log.info(), etc.

              # Check the resulting log messages.
              self.assertLog(["INFO: expected message #1",
                              "WARNING: expected message #2"])
    """

    def setUp(self):
        self._log = LogTesting.setUp(self)

    def set_logging_level(self, logging_level):
        self._log = LogTesting.setUp(self, logging_level=logging_level)

    def tearDown(self):
        self._log.tearDown()

    def logMessages(self):
        """Return the current list of log messages."""
        return self._log.messages()

    # Note: If there's a case where the caller deliberately doesn't
    # want to assert every message, a clearMessages() method could
    # be added here.

    # See the docstring for LogTesting.assertMessages() for an explanation
    # of why we clear the array of messages after asserting its contents.
    def assertLog(self, messages):
        """Asserts the current array of log messages, and clear its contents."""
        self._log.assertMessages(messages)