tests: Fix history patch window

Signed-off-by: Marek Siarkowicz <siarkowicz@google.com>

tests/linearizability/history.go

@@ -284,12 +284,14 @@ func (h history) Operations() []porcupine.Operation {
 			maxTime = op.Return
 		}
 	}
-	// Failed requests don't have a known return time.
-	// We simulate Infinity by using return time of latest successfully request.
 	for _, op := range h.failed {
 		if op.Call > maxTime {
-			continue
+			maxTime = op.Call
 		}
+	}
+	// Failed requests don't have a known return time.
+	// Simulate Infinity by using last observed time.
+	for _, op := range h.failed {
 		op.Return = maxTime + 1
 		operations = append(operations, op)
 	}

tests/linearizability/linearizability_test.go

@@ -143,11 +143,11 @@ func patchOperationBasedOnWatchEvents(operations []porcupine.Operation, watchEve
 	for _, op := range watchEvents {
 		persisted[op.Op] = op
 	}
-	lastObservedEventTime := watchEvents[len(watchEvents)-1].Time
+	lastObservedOperation := lastOperationObservedInWatch(operations, persisted)
 
 	for _, op := range operations {
 		resp := op.Output.(EtcdResponse)
-		if resp.Err == nil || op.Call > lastObservedEventTime.UnixNano() {
+		if resp.Err == nil || op.Call > lastObservedOperation.Call {
 			// No need to patch successfully requests and cannot patch requests outside observed window.
 			newOperations = append(newOperations, op)
 			continue
@@ -173,6 +173,19 @@ func patchOperationBasedOnWatchEvents(operations []porcupine.Operation, watchEve
 	return newOperations
 }
 
+func lastOperationObservedInWatch(operations []porcupine.Operation, watchEvents map[EtcdOperation]watchEvent) porcupine.Operation {
+	var maxCallTime int64
+	var lastOperation porcupine.Operation
+	for _, op := range operations {
+		event, _ := matchWatchEvent(op, watchEvents)
+		if event != nil && op.Call > maxCallTime {
+			maxCallTime = op.Call
+			lastOperation = op
+		}
+	}
+	return lastOperation
+}
+
 func matchWatchEvent(op porcupine.Operation, watchEvents map[EtcdOperation]watchEvent) (event *watchEvent, hasUniqueWriteOperation bool) {
 	request := op.Input.(EtcdRequest)
 	for _, etcdOp := range request.Ops {