tst: logs of previous bot runs survived until the next bot run

strip nullbytes from first line of bot log
truncate log_stream before initializing bot instance
ignore rare errors when the logs of the previous bot run appears in the logs of the current bot run

intelmq/lib/test.py

@@ -237,6 +237,13 @@ def prepare_bot(self, parameters={}, destination_queues=None, prepare_source_que
                         new=self.mocked_config):
             with mock.patch('intelmq.lib.utils.log', self.get_mocked_logger(self.logger)):
                 with mock.patch('intelmq.lib.utils.get_global_settings', mocked_get_global_settings):
+                    """
+                    Since Bot.__del__ method calls Bot.stop, log messages of the previous bot run like:
+                    "Processed/Forwarded X messages since last logging."
+                    "Bot stopped"
+                    appear in the log_stream at this point. So we clean the log before calling the bot, so that the tests in run_bot succeed.
+                    """
+                    self.log_stream.truncate(0)
                     self.bot = self.bot_reference(self.bot_id)
         self.bot._Bot__stats_cache = None
 
@@ -359,10 +366,10 @@ def run_bot(self, iterations: int = 1, error_on_pipeline: bool = False,
         try:
             self.assertLoglineMatches(0, BOT_INIT_REGEX.format(self.bot_name,
                                                                self.bot_id), "INFO")
-        except AssertionError:
-            if version_info <= (3, 8):
-                # In Python 3.7, the logging of the previous bot run can end up in the logging of the next run, resulting in line 0 being:
-                # "Processed 1 messages since last logging." (written at shutdown of that bot)
+        except AssertionError as exc:
+            # In some obscure but rate instances the logging of the previous bot run can end up in the logging of the next run, resulting in line 0 being:
+            # "Processed/Forwarded 1 messages since last logging." (written at shutdown of that previous bot run)
+            if 'since last logging' in exc.args[0]:
                 pass
             else:
                 raise
@@ -497,7 +504,7 @@ def assertLoglineMatches(self, line_no: int, pattern: str, levelname: str = "ERR
 
         self.assertIsNotNone(self.loglines)
         logline = self.loglines[line_no]
-        fields = utils.parse_logline(logline)
+        fields = utils.parse_logline(logline.strip('\x00'))
 
         self.assertEqual(self.bot_id, fields["bot_id"],
                          "bot_id {!r} didn't match {!r}."