Add test for empty data in PeriodGroupedData

If an empty data array is passed to a query with a duration parameter, currently we get a Python exception. This fixes that error.
alphagov · Jul 15, 2014 · c0dedcc · c0dedcc
1 parent 68ee108
commit c0dedcc
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diff --git a/backdrop/core/response.py b/backdrop/core/response.py
@@ -152,6 +152,9 @@ def fill_missing_periods(self, start_date, end_date, collect=None):
     def amount_to_shift(self, delta):
         is_reversed = delta < 0
 
+        if len(self._data) == 0:
+            return 0
+
         return min([
             first_nonempty(i['values'], is_reversed) for i in self._data],
             key=abs)
diff --git a/tests/read/test_weekly_grouped_data.py b/tests/read/test_weekly_grouped_data.py
@@ -86,3 +86,7 @@ def test_filling_data_for_missing_weeks(self):
             has_entry("_start_at", d_tz(2013, 4, 8)),
             has_entry("_start_at", d_tz(2013, 4, 15))
         ))
+
+    def test_with_empty_data(self):
+        data = PeriodGroupedData([], WEEK)
+        assert_that(data.amount_to_shift(7), equal_to(0))