add NSE sources to EX project to easily implement mocking and allow the code to be unit tested

UnitTests/Sources/NotificationContentBuilderTests.swift

@@ -0,0 +1,39 @@
+//
+// Copyright 2025 Element Creations Ltd.
+//
+// SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+// Please see LICENSE files in the repository root for full details.
+//
+
+import MatrixRustSDK
+import XCTest
+
+@testable import ElementX
+
+final class NotificationContentBuilderTests: XCTestCase {
+    var notificationContentBuilder: NotificationContentBuilder!
+    var mediaProvider: MediaProviderMock!
+    
+    override func setUp() {
+        let stringBuilder = RoomMessageEventStringBuilder(attributedStringBuilder: AttributedStringBuilder(mentionBuilder: PlainMentionBuilder()),
+                                                          destination: .notification)
+        mediaProvider = MediaProviderMock(configuration: .init())
+        notificationContentBuilder = NotificationContentBuilder(messageEventStringBuilder: stringBuilder,
+                                                                userSession: NSEUserSessionMock(.init()))
+    }
+    
+    func testDMMessageNotification() async {
+        let notificationItem = NotificationItemProxyMock(.init(senderDisplayName: "Alice",
+                                                               roomDisplayName: "Alice",
+                                                               roomJoinedMembers: 2,
+                                                               isRoomDirect: true,
+                                                               isRoomPrivate: true))
+        var notificationContent = UNMutableNotificationContent()
+        await notificationContentBuilder.process(notificationContent: &notificationContent,
+                                                 notificationItem: notificationItem,
+                                                 mediaProvider: mediaProvider)
+        
+        XCTAssertEqual(notificationContent.title, "Alice")
+        XCTAssertEqual(notificationContent.body, "Hello world!")
+    }
+}