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| # |
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| # in the documentation and/or other materials provided with the |
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| |
| """Code for instructing systems under test to block or fail.""" |
| |
| import abc |
| import contextlib |
| import threading |
| |
| import six |
| |
| |
| class Defect(Exception): |
| """Simulates a programming defect raised into in a system under test. |
| |
| Use of a standard exception type is too easily misconstrued as an actual |
| defect in either the test infrastructure or the system under test. |
| """ |
| |
| |
| class Control(six.with_metaclass(abc.ABCMeta)): |
| """An object that accepts program control from a system under test. |
| |
| Systems under test passed a Control should call its control() method |
| frequently during execution. The control() method may block, raise an |
| exception, or do nothing, all according to the enclosing test's desire for |
| the system under test to simulate hanging, failing, or functioning. |
| """ |
| |
| @abc.abstractmethod |
| def control(self): |
| """Potentially does anything.""" |
| raise NotImplementedError() |
| |
| |
| class PauseFailControl(Control): |
| """A Control that can be used to pause or fail code under control. |
| |
| This object is only safe for use from two threads: one of the system under |
| test calling control and the other from the test system calling pause, |
| block_until_paused, and fail. |
| """ |
| |
| def __init__(self): |
| self._condition = threading.Condition() |
| self._pause = False |
| self._paused = False |
| self._fail = False |
| |
| def control(self): |
| with self._condition: |
| if self._fail: |
| raise Defect() |
| |
| while self._pause: |
| self._paused = True |
| self._condition.notify_all() |
| self._condition.wait() |
| self._paused = False |
| |
| @contextlib.contextmanager |
| def pause(self): |
| """Pauses code under control while controlling code is in context.""" |
| with self._condition: |
| self._pause = True |
| yield |
| with self._condition: |
| self._pause = False |
| self._condition.notify_all() |
| |
| def block_until_paused(self): |
| """Blocks controlling code until code under control is paused. |
| |
| May only be called within the context of a pause call. |
| """ |
| with self._condition: |
| while not self._paused: |
| self._condition.wait() |
| |
| @contextlib.contextmanager |
| def fail(self): |
| """Fails code under control while controlling code is in context.""" |
| with self._condition: |
| self._fail = True |
| yield |
| with self._condition: |
| self._fail = False |