Always force a single value for firstresult hooks

Ensures that wrappers receive a single value instead of a list.

Fixes #71

Author: Tyler Goodlet

pluggy/callers.py

@@ -97,6 +97,10 @@ def execute(self):
                 excinfo = sys.exc_info()
         finally:
             outcome = _Result(results, excinfo)
+            if firstresult:  # first result hooks return a single value
+                results = outcome.get_result()
+                result = results[0] if results else None
+                outcome.force_result(result)
 
             # run all wrapper post-yield blocks
             for gen in reversed(teardowns):
@@ -106,10 +110,6 @@ def execute(self):
                 except StopIteration:
                     pass
 
-            if firstresult:
-                result = outcome.get_result()
-                return result[0] if result else None
-
             return outcome.get_result()
 
     def __repr__(self):