diff --git a/CalenTask/Services/CalendarSyncService.swift b/CalenTask/Services/CalendarSyncService.swift
index 9091a92..650acf2 100644
--- a/CalenTask/Services/CalendarSyncService.swift
+++ b/CalenTask/Services/CalendarSyncService.swift
@@ -431,10 +431,7 @@ final class CalendarSyncService {
         if let existing = localEvent(for: task) {
             event = existing.event
             span = existing.span
-        } else if linkedKey.flatMap(EventLinkRegistry.occurrence(fromKey:)) != nil
-                    || (task.eventIdentifier != nil && linkedKey == nil) {
-            // #1 — linked to ANOTHER device's event that isn't here (yet), or
-            // #2 an occurrence not found: a new event would be a duplicate.
+        } else if !Self.mayCreateEvent(linkedKey: linkedKey, syncedIdentifier: task.eventIdentifier) {
             return
         } else {
             span = .futureEvents
@@ -488,6 +485,14 @@ final class CalendarSyncService {
         }
     }
 
+    /// #1 — Se l'evento locale manca, crearne uno nuovo è lecito solo se la
+    /// task non è collegata a un evento di un ALTRO dispositivo (non ancora
+    /// arrivato qui) e #2 non è un'occorrenza non trovata: sarebbe un doppione.
+    static func mayCreateEvent(linkedKey: String?, syncedIdentifier: String?) -> Bool {
+        if linkedKey.flatMap(EventLinkRegistry.occurrence(fromKey:)) != nil { return false }
+        return syncedIdentifier == nil || linkedKey != nil
+    }
+
     private func removeRemoteEvent(for task: TodoTask) throws {
         guard let local = localEvent(for: task) else { return }
         let key = links.eventIdentifier(forTask: task.id)
diff --git a/CalenTask/Services/NotificationService.swift b/CalenTask/Services/NotificationService.swift
index ff66dbf..570f46f 100644
--- a/CalenTask/Services/NotificationService.swift
+++ b/CalenTask/Services/NotificationService.swift
@@ -53,11 +53,7 @@ final class NotificationService {
             Log.store.error("Riallineamento notifiche saltato: \(String(describing: error), privacy: .public)")
             return
         }
-        let now = Date.now
-        let planned = tasks
-            .flatMap { Self.plannedRequests(for: NotificationPlan(task: $0), now: now) }
-            .sorted { $0.fireDate < $1.fireDate }
-            .prefix(Self.maxPendingTaskRequests)
+        let planned = Self.nearestRequests(for: tasks, now: .now)
         resyncGeneration += 1
         let generation = resyncGeneration
         Task {
@@ -161,6 +157,19 @@ final class NotificationService {
             .map { ($0.request.identifier, $0.fireDate) }
     }
 
+    /// Identificatori e orari che `resyncAll` programmerebbe ora (per i test).
+    static func resyncSchedule(for tasks: [TodoTask], now: Date = .now) -> [(id: String, fireDate: Date)] {
+        nearestRequests(for: tasks, now: now).map { ($0.request.identifier, $0.fireDate) }
+    }
+
+    /// Le richieste più vicine di tutte le attività, entro il limite di sistema.
+    private static func nearestRequests(for tasks: [TodoTask], now: Date) -> [PlannedRequest] {
+        Array(tasks
+            .flatMap { plannedRequests(for: NotificationPlan(task: $0), now: now) }
+            .sorted { $0.fireDate < $1.fireDate }
+            .prefix(maxPendingTaskRequests))
+    }
+
     private static func plannedRequests(for plan: NotificationPlan, now: Date) -> [PlannedRequest] {
         guard plan.isActive else { return [] }
         var planned: [PlannedRequest] = []
diff --git a/CalenTaskTests/NotificationSyncTests.swift b/CalenTaskTests/NotificationSyncTests.swift
new file mode 100644
index 0000000..3b761a6
--- /dev/null
+++ b/CalenTaskTests/NotificationSyncTests.swift
@@ -0,0 +1,91 @@
+import Foundation
+import Testing
+@testable import CalenTask
+
+/// #19 — test sulle parti critiche: piano delle notifiche e decisioni della
+/// sync EventKit che non richiedono un `EKEventStore`.
+@MainActor
+struct NotificationSyncTests {
+
+    /// #4 — promemoria, scadenza e "Parti ora" hanno id e orari attesi;
+    /// gli orari passati e le attività eliminate non notificano.
+    @Test func remindDueAndTravelAreScheduled() throws {
+        // Ora fissa a metà mattina: la scadenza non cade mai a mezzanotte (→ 9:00).
+        let now = try #require(Calendar.current.date(
+            bySettingHour: 10, minute: 7, second: 0, of: Date(timeIntervalSince1970: 1_790_000_000)
+        ))
+        let start = now.addingTimeInterval(3 * 3600)
+        let task = TodoTask(workspaceID: UUID(), title: "Sopralluogo", kind: .event,
+                            startAt: start,
+                            dueAt: now.addingTimeInterval(5 * 3600),
+                            remindAt: now.addingTimeInterval(3600),
+                            locationName: "Teatro", createdByID: UUID())
+        task.travelMinutes = 30
+
+        let schedule = NotificationService.plannedSchedule(for: task, now: now)
+        let byID = Dictionary(uniqueKeysWithValues: schedule.map { ($0.id, $0.fireDate) })
+        #expect(byID.count == 3)
+        #expect(byID[NotificationService.remindID(task.id)] == task.remindAt)
+        #expect(byID[NotificationService.dueID(task.id)] == task.dueAt)
+        #expect(byID[NotificationService.travelID(task.id)] == start.addingTimeInterval(-30 * 60))
+
+        // Promemoria già passato: resta solo il resto.
+        task.remindAt = now.addingTimeInterval(-60)
+        let ids = NotificationService.plannedSchedule(for: task, now: now).map { $0.id }
+        #expect(!ids.contains(NotificationService.remindID(task.id)))
+        #expect(ids.count == 2)
+
+        task.deletedAt = now
+        #expect(NotificationService.plannedSchedule(for: task, now: now).isEmpty)
+    }
+
+    /// #4 — il riallineamento tiene solo le richieste più vicine, ordinate,
+    /// entro il limite di sistema; le completate non contano.
+    @Test func resyncKeepsNearestRequestsWithinLimit() {
+        let now = Date.now
+        let workspace = UUID(), author = UUID()
+        let tasks = (0..<70).map { index in
+            TodoTask(workspaceID: workspace, title: "Task \(index)",
+                     remindAt: now.addingTimeInterval(TimeInterval((70 - index) * 3600)),
+                     createdByID: author)
+        }
+        let done = TodoTask(workspaceID: workspace, title: "Fatta", status: .done,
+                            remindAt: now.addingTimeInterval(60), createdByID: author)
+
+        let schedule = NotificationService.resyncSchedule(for: tasks + [done], now: now)
+        #expect(schedule.count == NotificationService.maxPendingTaskRequests)
+        #expect(zip(schedule, schedule.dropFirst()).allSatisfy { $0.fireDate <= $1.fireDate })
+        // La più vicina è l'ultima creata; le 10 più lontane restano fuori.
+        #expect(schedule.first?.id == NotificationService.remindID(tasks[69].id))
+        let ids = Set(schedule.map { $0.id })
+        #expect(!ids.contains(NotificationService.remindID(tasks[0].id)))
+        #expect(!ids.contains(NotificationService.remindID(done.id)))
+    }
+
+    @Test func alertSubtitles() {
+        #expect(NotificationService.alertSubtitle(minutesBefore: 0) == "Inizia ora")
+        #expect(NotificationService.alertSubtitle(minutesBefore: 15) == "Tra 15 min")
+        #expect(NotificationService.alertSubtitle(minutesBefore: 120) == "Tra 2 h")
+        #expect(NotificationService.alertSubtitle(minutesBefore: 90) == "Tra 1 h 30 min")
+        #expect(NotificationService.alertSubtitle(minutesBefore: 1440) == "Domani")
+        #expect(NotificationService.alertSubtitle(minutesBefore: 2880) == "Tra 2 giorni")
+    }
+
+    /// #1, #2 — senza evento locale se ne crea uno nuovo solo quando non
+    /// sarebbe un doppione di un evento di un altro dispositivo o di
+    /// un'occorrenza non trovata.
+    @Test func newEventOnlyWhenNotADuplicate() {
+        let occurrence = EventLinkRegistry.occurrenceKey(
+            series: "UID|riunione", occurrenceDate: Date(timeIntervalSince1970: 1_790_000_000)
+        )
+        // Mai sincronizzata: si crea.
+        #expect(CalendarSyncService.mayCreateEvent(linkedKey: nil, syncedIdentifier: nil))
+        // Collegata qui ma l'evento è sparito dal calendario: si ricrea.
+        #expect(CalendarSyncService.mayCreateEvent(linkedKey: "EV-1", syncedIdentifier: "EV-1"))
+        // Evento di un altro dispositivo non ancora arrivato: niente doppione.
+        #expect(!CalendarSyncService.mayCreateEvent(linkedKey: nil, syncedIdentifier: "EV-MAC"))
+        // Occorrenza di una serie non trovata: niente evento nuovo.
+        #expect(!CalendarSyncService.mayCreateEvent(linkedKey: occurrence, syncedIdentifier: "EV-1"))
+        #expect(!CalendarSyncService.mayCreateEvent(linkedKey: occurrence, syncedIdentifier: nil))
+    }
+}