Fixed the optimization in the catalog that iterates over the sort index

rather than the result set when the result set is much larger than the
sort index.  Added a test and cleaned up the test framework.

lib/python/Products/ZCatalog/Catalog.py

@@ -23,7 +23,7 @@ from zLOG import LOG, ERROR
 from Lazy import LazyMap, LazyFilter, LazyCat
 from CatalogBrains import AbstractCatalogBrain, NoBrainer
 
-from BTrees.IIBTree import intersection, weightedIntersection
+from BTrees.IIBTree import intersection, weightedIntersection, IISet
 from BTrees.OIBTree import OIBTree
 from BTrees.IOBTree import IOBTree
 import BTrees.Length
@@ -549,9 +549,19 @@ class Catalog(Persistent, Acquisition.Implicit, ExtensionClass.Base):
         if (len(rs) > (len(sort_index) * 4)):
             # The result set is much larger than the sorted index,
             # so iterate over the sorted index for speed.
+
+            try:
+                intersection(rs, IISet(()))
+            except TypeError:
+                # rs is not an object in the IIBTree family.
+                # Try to turn rs into an IISet.
+                if hasattr(rs, 'keys'):
+                    rs = rs.keys()
+                rs = IISet(rs)
+
             for k, intset in sort_index.items():
                 # We have an index that has a set of values for
-                # each sort key, so we interset with each set and
+                # each sort key, so we intersect with each set and
                 # get a sorted sequence of the intersections.
                 intset = _intersection(rs, intset)
                 if intset:
@@ -630,7 +640,8 @@ class Catalog(Persistent, Acquisition.Implicit, ExtensionClass.Base):
         used = self._indexedSearch(args, sort_index, r.append, used)
         if not _merge:
             # Postpone merging and sorting.  This provides a way to
-            # sort results merged from multiple catalogs.
+            # efficiently sort results merged from multiple queries
+            # or multiple catalogs.
             return r
         else:
             has_sort_keys = 0

lib/python/Products/ZCatalog/tests/testCatalog.py

@@ -307,6 +307,14 @@ class TestCatalogObject(unittest.TestCase):
         a = self._catalog(att3='att3', att2='att2')
         assert len(a) == self.upper
 
+    def testLargeSortedResultSetWithSmallIndex(self):
+        # This exercises the optimization in the catalog that iterates
+        # over the sort index rather than the result set when the result
+        # set is much larger than the sort index.
+        a = self._catalog(sort_on='att1')
+        self.assertEqual(len(a), self.upper)
+        
+
 class objRS(ExtensionClass.Base):
 
     def __init__(self,num):
@@ -350,8 +358,5 @@ def test_suite():
     suite.addTest( unittest.makeSuite( testRS ) )
     return suite
 
-def main():
-    unittest.TextTestRunner().run(test_suite())
-
 if __name__ == '__main__':
-    main()
+    unittest.main(defaultTest='test_suite')