Simplify check for re-raised exception. Add tests.

scrapy/core/spidermw.py

@@ -103,7 +103,7 @@ class SpiderMiddlewareManager(MiddlewareManager):
                         yield r
                 except Exception as ex:
                     exception_result = process_spider_exception(Failure(ex), index+1)
-                    if exception_result is None or isinstance(exception_result, Failure):
+                    if isinstance(exception_result, Failure):
                         raise
                     recovered.extend(exception_result)
 
@@ -115,7 +115,7 @@ class SpiderMiddlewareManager(MiddlewareManager):
                     result = method(response=response, result=result, spider=spider)
                 except Exception as ex:
                     exception_result = process_spider_exception(Failure(ex), method_index+1)
-                    if exception_result is None or isinstance(exception_result, Failure):
+                    if isinstance(exception_result, Failure):
                         raise
                     return exception_result
                 if _isiterable(result):

tests/test_spidermiddleware.py

@@ -80,3 +80,23 @@ class ProcessSpiderExceptionInvalidOutput(SpiderMiddlewareTestCase):
         result = self._scrape_response()
         self.assertIsInstance(result, Failure)
         self.assertIsInstance(result.value, _InvalidOutput)
+
+
+class ProcessSpiderExceptionReRaise(SpiderMiddlewareTestCase):
+    """Re raise the exception by returning None"""
+
+    def test_process_spider_exception_return_none(self):
+
+        class ProcessSpiderOutputExceptionReturnNoneMiddleware:
+            def process_spider_exception(self, response, exception, spider):
+                return None
+
+        class RaiseExceptionProcessSpiderOutputMiddleware:
+            def process_spider_output(self, response, result, spider):
+                1/0
+
+        self.mwman._add_middleware(ProcessSpiderOutputExceptionReturnNoneMiddleware())
+        self.mwman._add_middleware(RaiseExceptionProcessSpiderOutputMiddleware())
+        result = self._scrape_response()
+        self.assertIsInstance(result, Failure)
+        self.assertIsInstance(result.value, ZeroDivisionError)