Avoid TypeError when running at PeriodicItemCountMonitor (#436)

* Avoid TypeError when running when PeriodicItemCountMonitor runs first time with undefined item_scraped_count stat

* Add success case

* Move None to 0 conversion place

spidermon/contrib/scrapy/monitors/monitors.py

@@ -632,7 +632,7 @@ def run(self, result):
     def get_threshold(self):
         crawler = self.data.crawler
         prev_item_scraped_count = self.stats.get("prev_item_scraped_count", 0)
-        item_scraped_count = self.stats.get(self.stat_name)
+        item_scraped_count = self.stats.get(self.stat_name, 0)
         crawler.stats.set_value("prev_item_scraped_count", item_scraped_count)
         threshold_increase = crawler.settings.get(self.threshold_setting)
         if isinstance(threshold_increase, int):

tests/contrib/scrapy/monitors/test_periodic_execution_time_monitor.py

@@ -136,3 +136,17 @@ def test_item_count_monitor_validation(
     runner.run(item_count_suite, **data)
     assert len(runner.result.monitor_results) == 1
     assert runner.result.monitor_results[0].status == expected_status
+
+
+def test_item_count_monitor_undefined_stats(make_data, item_count_suite):
+    data = make_data({SPIDERMON_ITEM_COUNT_INCREASE: 0})
+    data["stats"]["enable_stats"] = 1  # otherwise monitor wont run
+    runner = data.pop("runner")
+    runner.run(MonitorSuite(monitors=[PeriodicItemCountMonitor]), **data)
+    assert runner.result.monitor_results[0].status == settings.MONITOR.STATUS.FAILURE
+    runner.run(MonitorSuite(monitors=[PeriodicItemCountMonitor]), **data)
+    assert runner.result.monitor_results[0].status == settings.MONITOR.STATUS.FAILURE
+
+    data["stats"]["item_scraped_count"] = 1
+    runner.run(MonitorSuite(monitors=[PeriodicItemCountMonitor]), **data)
+    assert runner.result.monitor_results[0].status == settings.MONITOR.STATUS.SUCCESS