Test for mixed failure of classifyChanges

Test for an insert failure midway through a classification, in which
case the rollback shouldn't roll back any successful inserts.

Fixes #2696.

(Backport of d8d3753)

master/buildbot/db/schedulers.py

@@ -24,13 +24,13 @@ class SchedulersConnectorComponent(base.DBConnectorComponent):
 
     def classifyChanges(self, objectid, classifications):
         def thd(conn):
-            transaction = conn.begin()
             tbl = self.db.model.scheduler_changes
             ins_q = tbl.insert()
             upd_q = tbl.update(
                 ((tbl.c.objectid == objectid)
                  & (tbl.c.changeid == sa.bindparam('wc_changeid'))))
             for changeid, important in classifications.items():
+                transaction = conn.begin()
                 # convert the 'important' value into an integer, since that
                 # is the column type
                 imp_int = important and 1 or 0
@@ -48,7 +48,7 @@ def thd(conn):
                                  wc_changeid=changeid,
                                  important=imp_int)
 
-            transaction.commit()
+                transaction.commit()
         return self.db.pool.do(thd)
 
     def flushChangeClassifications(self, objectid, less_than=None):

master/buildbot/test/unit/test_db_schedulers.py

@@ -85,14 +85,21 @@ def thd(conn):
 
     def test_classifyChanges_again(self):
         # test reclassifying changes, which may happen during some timing
-        # conditions
+        # conditions.  It's important that this test uses multiple changes,
+        # only one of which already exists
         d = self.insertTestData([
+        # conditions.  It's important that this test uses multiple changes,
+        # only one of which already exists
             self.change3,
+            self.change4,
+            self.change5,
+            self.change6,
             self.scheduler24,
-            fakedb.SchedulerChange(objectid=24, changeid=3, important=0),
+            fakedb.SchedulerChange(objectid=24, changeid=5, important=0),
         ])
         d.addCallback(lambda _:
-                      self.db.schedulers.classifyChanges(24, {3: True}))
+                      self.db.schedulers.classifyChanges(
+                          24, {3: True, 4: False, 5: True, 6: False}))
 
         def check(_):
             def thd(conn):
@@ -101,7 +108,9 @@ def thd(conn):
                 r = conn.execute(q)
                 rows = [(row.objectid, row.changeid, row.important)
                         for row in r.fetchall()]
-                self.assertEqual(rows, [(24, 3, 1)])
+                self.assertEqual(sorted(rows),
+                                 sorted([(24, 3, 1), (24, 4, 0),
+                                         (24, 5, 1), (24, 6, 0)]))
             return self.db.pool.do(thd)
         d.addCallback(check)
         return d