Fix truncation tests

datadog_checks_base/tests/test_db_statements.py

@@ -97,17 +97,17 @@ def key(row):
         ]
         # Simulate a stats reset by decreasing one of the metrics rather than increasing
         rows3 = [
-            add_to_dict(rows2[1], {'count': 1, 'time': 15, 'errors': 0}),
             add_to_dict(rows2[0], {'count': -1, 'time': 0, 'errors': 15}),
+            add_to_dict(rows2[1], {'count': 1, 'time': 15, 'errors': 0}),
         ]
         rows4 = [
-            add_to_dict(rows3[1], {'count': 1, 'time': 1, 'errors': 0}),
             add_to_dict(rows3[0], {'count': 1, 'time': 1, 'errors': 1}),
+            add_to_dict(rows3[1], {'count': 1, 'time': 1, 'errors': 0}),
         ]
         assert [] == sm.compute_derivative_rows(rows1, metrics, key=key)
-        assert 2 == len(sm.compute_derivative_rows(rows2, metrics, key=key))
-        assert [] == sm.compute_derivative_rows(rows3, metrics, key=key)
-        assert 2 == len(sm.compute_derivative_rows(rows4, metrics, key=key))
+        assert 2 == len(sm.compute_derivative_rows(rows2, metrics, key=key))  # both rows computed
+        assert 1 == len(sm.compute_derivative_rows(rows3, metrics, key=key))  # only 1 row computed
+        assert 2 == len(sm.compute_derivative_rows(rows4, metrics, key=key))  # both rows computed
 
     def test_apply_row_limits(self):
         def assert_any_order(a, b):