def flushTracebacks(self, exceptionType):
        """
        Flush all logged tracebacks whose exception is of the given type.

        This means they are expected tracebacks and should not cause the test
        to fail.

        @param exceptionType: A subclass of L{Exception}.

        @return: C{list} of flushed messages.
        """
        result = []
        remaining = []
        for message in self.tracebackMessages:
            if isinstance(message[REASON_FIELD], exceptionType):
                result.append(message)
            else:
                remaining.append(message)
        self.tracebackMessages = remaining
        return result