diff --git a/impl/e2e-tests/lookback.json b/impl/e2e-tests/lookback.json
new file mode 100644
index 0000000..a654f01
--- /dev/null
+++ b/impl/e2e-tests/lookback.json
@@ -0,0 +1,63 @@
+{
+  "$comment": "use different advertiser sites to avoid depending on budgeting",
+  "events": [
+    {
+      "seconds": 1,
+      "site": "publisher.example",
+      "event": "saveImpression",
+      "options": { "histogramIndex": 1 }
+    },
+    {
+      "seconds": 2,
+      "site": "publisher.example",
+      "intermediarySite": "adtech.example",
+      "event": "saveImpression",
+      "options": { "histogramIndex": 2 }
+    },
+    {
+      "seconds": 86402,
+      "site": "advertiser-1.example",
+      "event": "measureConversion",
+      "$comment": "try to select 2 impressions to avoid depending on ordering",
+      "options": {
+        "aggregationService": "https://agg-service.example",
+        "histogramSize": 3,
+        "lookbackDays": 1,
+        "value": 2,
+        "maxValue": 2,
+        "credit": [0.5, 0.5]
+      },
+      "expected": [0, 0, 2]
+    },
+    {
+      "seconds": 172802,
+      "site": "advertiser-2.example",
+      "event": "measureConversion",
+      "$comment": "try to select 2 impressions to avoid depending on ordering",
+      "options": {
+        "aggregationService": "https://agg-service.example",
+        "histogramSize": 3,
+        "lookbackDays": 1,
+        "value": 2,
+        "maxValue": 2,
+        "credit": [0.5, 0.5]
+      },
+      "expected": [0, 0, 0]
+    },
+    {
+      "seconds": 172803,
+      "site": "advertiser-3.example",
+      "event": "measureConversion",
+      "$comment": "try to select 2 impressions to avoid depending on ordering",
+      "options": {
+        "aggregationService": "https://agg-service.example",
+        "histogramSize": 3,
+        "lookbackDays": 3,
+        "value": 2,
+        "maxValue": 2,
+        "credit": [0.5, 0.5]
+      },
+      "expected": [0, 1, 1]
+    }
+  ]
+}