[LNT] Python 3 support: sort benchmark regressing

[thopre]

Summary

Test server/ui/change_processing.py makes an assumption about the order
in which benchmark are listed when a regression occurs but these are put
in a set before being iterated over for printing. Since set have no
guarantee of order, the test is fragile and fails on Python 3 due to
different implementation of Set. This commit sort the benchmark when
printing them so that the output is consistent. It also adapts the
testcase accordingly.

[PrzemekWirkus]

tests/server/ui/change_processing.py

214–216

I would still add a comment here that "bar, foo" should be in alphabetical order to mach assert with sorted().

[thopre]

Add comment to explain assumptions

tests/server/ui/change_processing.py

214–216

Good point.

[thopre]

Committed as d836856b7ff9be352f19faa90a16be2b05d0e4bb

lnt/server/db/regression.py

if re.match(r"Regression of \d+ benchmarks.*", regression.title):
             .filter(ts.RegressionIndicator.regression_id == regression.id) \
             .all()
         new_size = len(old_changes)
         benchmarks = set()
         for ri in old_changes:
             fc = ri.field_change
             benchmarks.add(shortname(fc.test.name))
         FMT = "Regression of {} benchmarks: {}"
-        title = FMT.format(new_size, ', '.join(benchmarks))
+        title = FMT.format(new_size, ', '.join(sorted(benchmarks)))
         # Crop long titles.
         title = (title[:120] + '...') if len(title) > 120 else title
         regression.title = title
     return regression
 
 
 def get_all_orders_for_machine(session, ts, machine):
     """Get all the orders for this sa machine."""

tests/server/ui/change_processing.py

def test_change_grouping_criteria(self):
                                           self.a_field2.id)
 
         # Check a regression matches if all fields match.
         ret, _ = identify_related_changes(session, ts_db, field_change6, active_indicators)
         self.assertTrue(ret, "Should Match with different fields.")
 
         session.commit()
 
         r2 = rebuild_title(session, ts_db, self.regression)
-        expected_title = "Regression of 6 benchmarks: foo, bar"
+        # The list of benchmark regressing is guaranteed to be sorted.
+        expected_title = "Regression of 6 benchmarks: bar, foo"
         self.assertEqual(r2.title, expected_title)
 
     def test_regression_evolution(self):
         session = self.session
         ts_db = self.ts_db
         rule_update_fixed_regressions.regression_evolution(
             session, ts_db, self.run.id)