fix issue 188 - ensure sys.exc_info on py2 is clear before calling into a test

CHANGELOG

@@ -56,6 +56,9 @@ Changes between 2.2.4 and 2.3.0.dev
 
 - fix issue 182: testdir.inprocess_run now considers passed plugins
 
+- fix issue 188: ensure sys.exc_info is clear on python2
+                 before calling into a test
+
 - reporting refinements:
 
   - pytest_report_header now receives a "startdir" so that

_pytest/main.py

@@ -114,11 +114,18 @@ def pytest_collection(session):
 def pytest_runtestloop(session):
     if session.config.option.collectonly:
         return True
-    for i, item in enumerate(session.items):
+
+    def getnextitem(i):
+        # this is a function to avoid python2
+        # keeping sys.exc_info set when calling into a test
+        # python2 keeps sys.exc_info till the frame is left
         try:
-            nextitem = session.items[i+1]
+            return session.items[i+1]
         except IndexError:
-            nextitem = None
+            return None
+
+    for i, item in enumerate(session.items):
+        nextitem = getnextitem(i)
         item.config.hook.pytest_runtest_protocol(item=item, nextitem=nextitem)
         if session.shouldstop:
             raise session.Interrupted(session.shouldstop)

testing/test_runner.py

@@ -180,7 +180,12 @@ class BaseFunctionalTests:
                     raise Exception()
 
             def test_func():
-                pass
+                import sys
+                # on python2 exc_info is keept till a function exits
+                # so we would end up calling test functions while
+                # sys.exc_info would return the indexerror
+                # from guessing the lastitem
+                assert sys.exc_info()[0] is None
             def teardown_function(func):
                 raise ValueError(42)
         """)