[LNT] fix ValueError in corner case

[danilaml]

Summary

Fixes ValueError('need more than 0 values to unpack',) that could appear in some corner cases (the fewer runs you have in your db the more likely you'll encounter it).

[cmatthews]

LGTM. Thanks!

lnt/trunk/lnt/server/reporting/analysis.py

def get_comparison_result(self, runs, compare_runs, test_id, field,
                              run_failed, prev_failed, run_values,
                              prev_values, cur_hash, prev_hash,
                              cur_profile, prev_profile,
                              self.confidence_lv,
                              bigger_is_better=field.bigger_is_better)
         return r
 
     def get_geomean_comparison_result(self, run, compare_to, field, tests):
-        if tests:
-            prev_values, run_values, prev_hash, cur_hash = zip(
-                *[(cr.previous, cr.current, cr.prev_hash, cr.cur_hash)
+        unchanged_tests = [(cr.previous, cr.current, cr.prev_hash, cr.cur_hash)
                            for _, _, cr in tests
-                  if cr.get_test_status() == UNCHANGED_PASS])
+                           if cr.get_test_status() == UNCHANGED_PASS]
+        if unchanged_tests:
+            prev_values, run_values, prev_hash, cur_hash = zip(
+                *unchanged_tests)
             prev_values = [x for x in prev_values if x is not None]
             run_values = [x for x in run_values if x is not None]
             prev_hash = [x for x in prev_hash if x is not None]
             cur_hash = [x for x in cur_hash if x is not None]
             prev_hash = prev_hash[0] if len(prev_hash) > 0 else None
             cur_hash = cur_hash[0] if len(cur_hash) > 0 else None
             prev_geo = calc_geomean(prev_values)
             prev_values = [prev_geo] if prev_geo else []

lnt/trunk/tests/server/ui/V4Pages.py

 # Perform basic sanity checking of the V4 UI pages.
 #
 # create temporary instance
 # Cleanup temporary directory in case one remained from a previous run - also
 # see PR9904.
 # RUN: rm -rf %t.instance
 # RUN: python %{shared_inputs}/create_temp_instance.py \
 # RUN:   %s %{shared_inputs}/SmallInstance %t.instance \
 # RUN:   %S/Inputs/V4Pages_extra_records.sql
 
 # Import a profile
 # RUN: lnt import %t.instance %{shared_inputs}/profile-report.json
 #
+# RUN: lnt import %t.instance %S/Inputs/sample-failed-report1.json
+# RUN: lnt import %t.instance %S/Inputs/sample-failed-report2.json
+#
 # RUN: python %s %t.instance %{tidylib}
 
 import logging
 import re
 import sys
 import xml.etree.ElementTree as ET
 from htmlentitydefs import name2codepoint
 from flask import session
def main():
     assert graph_to_sample.headers['Location'] == "http://localhost/db_default/v4/nts/graph?foo=bar&plot.0=2.6.0"
 
     # Check that is we ask for a sample or invalid field, we explode with 400s.
     check_code(client, '/db_default/v4/nts/graph_for_sample/10000/compile_time?foo=bar',
                expected_code=HTTP_NOT_FOUND)
     check_code(client, '/db_default/v4/nts/graph_for_sample/10/not_a_metric?foo=bar',
                expected_code=HTTP_BAD_REQUEST)
 
+    # check get_geomean_comparison_result with empty unchanged_tests
+    check_html(client, '/v4/nts/11')
+    check_html(client, '/v4/nts/12')
+
 
 if __name__ == '__main__':
     main()