Merge pull request #931 from permissionlesstech/fix/flaky-fragmentation-tests

fix: eliminate flaky FragmentationTests with proper async synchronization

bitchat/Features/voice/VoiceRecorder.swift

@@ -58,11 +58,20 @@ final class VoiceRecorder: NSObject, AVAudioRecorderDelegate {
             guard session.recordPermission == .granted else {
                 throw RecorderError.microphoneAccessDenied
             }
+            #if targetEnvironment(simulator)
+            // allowBluetoothHFP is not available on iOS Simulator
+            try session.setCategory(
+                .playAndRecord,
+                mode: .default,
+                options: [.defaultToSpeaker, .allowBluetoothA2DP]
+            )
+            #else
             try session.setCategory(
                 .playAndRecord,
                 mode: .default,
                 options: [.defaultToSpeaker, .allowBluetoothA2DP, .allowBluetoothHFP]
             )
+            #endif
             try session.setActive(true, options: .notifyOthersOnDeactivation)
             #endif
             #if os(macOS)

bitchat/Noise/NoiseProtocol.swift

@@ -610,14 +610,20 @@ final class NoiseHandshakeState {
                         throw NoiseError.missingKeys
                     }
                     let shared = try localEphemeral.sharedSecretFromKeyAgreement(with: remoteStatic)
-                    symmetricState.mixKey(shared.withUnsafeBytes { Data($0) })
+                    var sharedData = shared.withUnsafeBytes { Data($0) }
+                    symmetricState.mixKey(sharedData)
+                    // Clear sensitive shared secret
+                    keychain.secureClear(&sharedData)
                 } else {
                     guard let localStatic = localStaticPrivate,
                           let remoteEphemeral = remoteEphemeralPublic else {
                         throw NoiseError.missingKeys
                     }
                     let shared = try localStatic.sharedSecretFromKeyAgreement(with: remoteEphemeral)
-                    symmetricState.mixKey(shared.withUnsafeBytes { Data($0) })
+                    var sharedData = shared.withUnsafeBytes { Data($0) }
+                    symmetricState.mixKey(sharedData)
+                    // Clear sensitive shared secret
+                    keychain.secureClear(&sharedData)
                 }
                 
             case .se:
@@ -628,14 +634,20 @@ final class NoiseHandshakeState {
                         throw NoiseError.missingKeys
                     }
                     let shared = try localStatic.sharedSecretFromKeyAgreement(with: remoteEphemeral)
-                    symmetricState.mixKey(shared.withUnsafeBytes { Data($0) })
+                    var sharedData = shared.withUnsafeBytes { Data($0) }
+                    symmetricState.mixKey(sharedData)
+                    // Clear sensitive shared secret
+                    keychain.secureClear(&sharedData)
                 } else {
                     guard let localEphemeral = localEphemeralPrivate,
                           let remoteStatic = remoteStaticPublic else {
                         throw NoiseError.missingKeys
                     }
                     let shared = try localEphemeral.sharedSecretFromKeyAgreement(with: remoteStatic)
-                    symmetricState.mixKey(shared.withUnsafeBytes { Data($0) })
+                    var sharedData = shared.withUnsafeBytes { Data($0) }
+                    symmetricState.mixKey(sharedData)
+                    // Clear sensitive shared secret
+                    keychain.secureClear(&sharedData)
                 }
                 
             case .ss:
@@ -724,8 +736,11 @@ final class NoiseHandshakeState {
                 throw NoiseError.missingKeys
             }
             let shared = try localEphemeral.sharedSecretFromKeyAgreement(with: remoteEphemeral)
-            symmetricState.mixKey(shared.withUnsafeBytes { Data($0) })
-            
+            var sharedData = shared.withUnsafeBytes { Data($0) }
+            symmetricState.mixKey(sharedData)
+            // Clear sensitive shared secret
+            keychain.secureClear(&sharedData)
+
         case .es:
             if role == .initiator {
                 guard let localEphemeral = localEphemeralPrivate,
@@ -778,8 +793,11 @@ final class NoiseHandshakeState {
                 throw NoiseError.missingKeys
             }
             let shared = try localStatic.sharedSecretFromKeyAgreement(with: remoteStatic)
-            symmetricState.mixKey(shared.withUnsafeBytes { Data($0) })
-            
+            var sharedData = shared.withUnsafeBytes { Data($0) }
+            symmetricState.mixKey(sharedData)
+            // Clear sensitive shared secret
+            keychain.secureClear(&sharedData)
+
         case .e, .s:
             break
         }

bitchat/Nostr/KeychainHelper.swift

@@ -1,50 +0,0 @@
-import Foundation
-
-protocol KeychainHelperProtocol {
-    func save(key: String, data: Data, service: String, accessible: CFString?)
-    func load(key: String, service: String) -> Data?
-    func delete(key: String, service: String)
-}
-
-/// Keychain helper for secure storage
-struct KeychainHelper: KeychainHelperProtocol {
-    func save(key: String, data: Data, service: String, accessible: CFString? = nil) {
-        var query: [String: Any] = [
-            kSecClass as String: kSecClassGenericPassword,
-            kSecAttrService as String: service,
-            kSecAttrAccount as String: key,
-            kSecValueData as String: data
-        ]
-        if let accessible = accessible {
-            query[kSecAttrAccessible as String] = accessible
-        }
-        
-        SecItemDelete(query as CFDictionary)
-        SecItemAdd(query as CFDictionary, nil)
-    }
-    
-    func load(key: String, service: String) -> Data? {
-        let query: [String: Any] = [
-            kSecClass as String: kSecClassGenericPassword,
-            kSecAttrService as String: service,
-            kSecAttrAccount as String: key,
-            kSecReturnData as String: true
-        ]
-        
-        var result: AnyObject?
-        let status = SecItemCopyMatching(query as CFDictionary, &result)
-        
-        guard status == errSecSuccess else { return nil }
-        return result as? Data
-    }
-    
-    func delete(key: String, service: String) {
-        let query: [String: Any] = [
-            kSecClass as String: kSecClassGenericPassword,
-            kSecAttrService as String: service,
-            kSecAttrAccount as String: key
-        ]
-        
-        SecItemDelete(query as CFDictionary)
-    }
-}

bitchat/Nostr/NostrIdentityBridge.swift

@@ -12,9 +12,9 @@ final class NostrIdentityBridge {
     private var derivedIdentityCache: [String: NostrIdentity] = [:]
     private let cacheLock = NSLock()
 
-    private let keychain: KeychainHelperProtocol
+    private let keychain: KeychainManagerProtocol
 
-    init(keychain: KeychainHelperProtocol = KeychainHelper()) {
+    init(keychain: KeychainManagerProtocol = KeychainManager()) {
         self.keychain = keychain
     }
     

bitchat/Protocols/BinaryEncodingUtils.swift

@@ -23,20 +23,42 @@ extension Data {
         return digest.map { String(format: "%02x", $0) }.joined()
     }
     
+    /// Initialize Data from a hex string.
+    /// - Parameter hexString: A hex string, optionally prefixed with "0x" or "0X".
+    ///   Whitespace is trimmed. Must have even length after prefix removal.
+    /// - Returns: nil if the string has odd length or contains invalid hex characters.
     init?(hexString: String) {
-        let len = hexString.count / 2
+        var hex = hexString.trimmingCharacters(in: .whitespaces)
+
+        // Remove optional 0x prefix
+        if hex.hasPrefix("0x") || hex.hasPrefix("0X") {
+            hex = String(hex.dropFirst(2))
+        }
+
+        // Reject odd-length strings
+        guard hex.count % 2 == 0 else {
+            return nil
+        }
+
+        // Reject empty strings
+        guard !hex.isEmpty else {
+            self = Data()
+            return
+        }
+
+        let len = hex.count / 2
         var data = Data(capacity: len)
-        var index = hexString.startIndex
-        
+        var index = hex.startIndex
+
         for _ in 0..<len {
-            let nextIndex = hexString.index(index, offsetBy: 2)
-            guard let byte = UInt8(String(hexString[index..<nextIndex]), radix: 16) else {
+            let nextIndex = hex.index(index, offsetBy: 2)
+            guard let byte = UInt8(String(hex[index..<nextIndex]), radix: 16) else {
                 return nil
             }
             data.append(byte)
             index = nextIndex
         }
-        
+
         self = data
     }
 }

bitchat/Services/FavoritesPersistenceService.swift

@@ -26,7 +26,7 @@ final class FavoritesPersistenceService: ObservableObject {
 
     private static let storageKey = "chat.bitchat.favorites"
     private static let keychainService = "chat.bitchat.favorites"
-    private let keychain: KeychainHelperProtocol
+    private let keychain: KeychainManagerProtocol
     
     @Published private(set) var favorites: [Data: FavoriteRelationship] = [:] // Noise pubkey -> relationship
     @Published private(set) var mutualFavorites: Set<Data> = []
@@ -35,8 +35,8 @@ final class FavoritesPersistenceService: ObservableObject {
     private var cancellables = Set<AnyCancellable>()
     
     static let shared = FavoritesPersistenceService()
-    
-    init(keychain: KeychainHelperProtocol = KeychainHelper()) {
+
+    init(keychain: KeychainManagerProtocol = KeychainManager()) {
         self.keychain = keychain
         loadFavorites()
         

bitchat/Services/KeychainManager.swift

@@ -15,11 +15,19 @@ protocol KeychainManagerProtocol {
     func getIdentityKey(forKey key: String) -> Data?
     func deleteIdentityKey(forKey key: String) -> Bool
     func deleteAllKeychainData() -> Bool
-    
+
     func secureClear(_ data: inout Data)
     func secureClear(_ string: inout String)
-    
+
     func verifyIdentityKeyExists() -> Bool
+
+    // MARK: - Generic Data Storage (consolidated from KeychainHelper)
+    /// Save data with a custom service name
+    func save(key: String, data: Data, service: String, accessible: CFString?)
+    /// Load data from a custom service
+    func load(key: String, service: String) -> Data?
+    /// Delete data from a custom service
+    func delete(key: String, service: String)
 }
 
 final class KeychainManager: KeychainManagerProtocol {
@@ -309,9 +317,54 @@ final class KeychainManager: KeychainManagerProtocol {
     }
     
     // MARK: - Debug
-    
+
     func verifyIdentityKeyExists() -> Bool {
         let key = "identity_noiseStaticKey"
         return retrieveData(forKey: key) != nil
     }
+
+    // MARK: - Generic Data Storage (consolidated from KeychainHelper)
+
+    /// Save data with a custom service name
+    func save(key: String, data: Data, service customService: String, accessible: CFString?) {
+        var query: [String: Any] = [
+            kSecClass as String: kSecClassGenericPassword,
+            kSecAttrService as String: customService,
+            kSecAttrAccount as String: key,
+            kSecValueData as String: data
+        ]
+        if let accessible = accessible {
+            query[kSecAttrAccessible as String] = accessible
+        }
+
+        SecItemDelete(query as CFDictionary)
+        SecItemAdd(query as CFDictionary, nil)
+    }
+
+    /// Load data from a custom service
+    func load(key: String, service customService: String) -> Data? {
+        let query: [String: Any] = [
+            kSecClass as String: kSecClassGenericPassword,
+            kSecAttrService as String: customService,
+            kSecAttrAccount as String: key,
+            kSecReturnData as String: true
+        ]
+
+        var result: AnyObject?
+        let status = SecItemCopyMatching(query as CFDictionary, &result)
+
+        guard status == errSecSuccess else { return nil }
+        return result as? Data
+    }
+
+    /// Delete data from a custom service
+    func delete(key: String, service customService: String) {
+        let query: [String: Any] = [
+            kSecClass as String: kSecClassGenericPassword,
+            kSecAttrService as String: customService,
+            kSecAttrAccount as String: key
+        ]
+
+        SecItemDelete(query as CFDictionary)
+    }
 }

bitchat/Services/MessageDeduplicationService.swift

@@ -12,6 +12,8 @@ import Foundation
 
 /// Generic LRU (Least Recently Used) cache for deduplication.
 /// Uses an efficient O(1) lookup with periodic compaction.
+/// Thread-safe via @MainActor - all callers are already on main actor.
+@MainActor
 final class LRUDeduplicationCache<Value> {
     private var map: [String: Value] = [:]
     private var order: [String] = []
@@ -157,6 +159,8 @@ enum ContentNormalizer {
 
 /// Service that manages message deduplication using LRU caches.
 /// Provides separate caches for content-based dedup and Nostr event ID dedup.
+/// Thread-safe via @MainActor - all callers are already on main actor.
+@MainActor
 final class MessageDeduplicationService {
 
     /// Cache for content-based near-duplicate detection

bitchat/Services/NostrTransport.swift

@@ -149,8 +149,11 @@ final class NostrTransport: Transport, @unchecked Sendable {
 
     func sendReadReceipt(_ receipt: ReadReceipt, to peerID: PeerID) {
         // Enqueue and process with throttling to avoid relay rate limits
-        readQueue.append(QueuedRead(receipt: receipt, peerID: peerID))
-        processReadQueueIfNeeded()
+        // Use barrier to synchronize access to readQueue
+        queue.async(flags: .barrier) { [weak self] in
+            self?.readQueue.append(QueuedRead(receipt: receipt, peerID: peerID))
+            self?.processReadQueueIfNeeded()
+        }
     }
 
     func sendFavoriteNotification(to peerID: PeerID, isFavorite: Bool) {
@@ -260,16 +263,17 @@ extension NostrTransport {
 // MARK: - Private Helpers
 
 extension NostrTransport {
+    /// Must be called within a barrier on `queue`
     private func processReadQueueIfNeeded() {
         guard !isSendingReadAcks else { return }
         guard !readQueue.isEmpty else { return }
         isSendingReadAcks = true
-        sendNextReadAck()
+        let item = readQueue.removeFirst()
+        sendReadAckItem(item)
     }
 
-    private func sendNextReadAck() {
-        guard !readQueue.isEmpty else { isSendingReadAcks = false; return }
-        let item = readQueue.removeFirst()
+    /// Sends a single read ack item (called after extraction from queue within barrier)
+    private func sendReadAckItem(_ item: QueuedRead) {
         Task { @MainActor in
             guard let recipientNpub = resolveRecipientNpub(for: item.peerID) else { scheduleNextReadAck(); return }
             guard let senderIdentity = try? idBridge.getCurrentNostrIdentity() else { scheduleNextReadAck(); return }
@@ -301,9 +305,10 @@ extension NostrTransport {
 
     private func scheduleNextReadAck() {
         DispatchQueue.main.asyncAfter(deadline: .now() + readAckInterval) { [weak self] in
-            guard let self = self else { return }
-            self.isSendingReadAcks = false
-            self.processReadQueueIfNeeded()
+            self?.queue.async(flags: .barrier) { [weak self] in
+                self?.isSendingReadAcks = false
+                self?.processReadQueueIfNeeded()
+            }
         }
     }
 

bitchat/Utils/MessageDeduplicator.swift

@@ -5,7 +5,7 @@ import Foundation
 /// Thread-safe deduplicator with LRU eviction and time-based expiry.
 /// Used for both message ID deduplication (network layer) and content key deduplication (UI layer).
 final class MessageDeduplicator {
-    private struct Entry {
+    private struct Entry: Equatable {
         let id: String
         let timestamp: Date
     }
@@ -31,18 +31,20 @@ final class MessageDeduplicator {
         self.maxCount = maxCount
     }
 
-    /// Check if message is duplicate and add if not
+    /// Check if message is duplicate and add if not.
+    /// - Parameter id: The message identifier to check.
+    /// - Returns: `true` if the message was already seen, `false` otherwise.
     func isDuplicate(_ id: String) -> Bool {
         lock.lock()
         defer { lock.unlock() }
 
-        cleanupOldEntries()
+        let now = Date()
+        cleanupOldEntries(before: now.addingTimeInterval(-maxAge))
 
         if lookup[id] != nil {
             return true
         }
 
-        let now = Date()
         entries.append(Entry(id: id, timestamp: now))
         lookup[id] = now
         trimIfNeeded()
@@ -89,18 +91,22 @@ final class MessageDeduplicator {
     }
 
     private func trimIfNeeded() {
-        // Soft-cap and advance head by a chunk to avoid O(n) shifting
-        if (entries.count - head) > maxCount {
-            let removeCount = min(100, entries.count - head)
-            for i in head..<(head + removeCount) {
-                lookup.removeValue(forKey: entries[i].id)
-            }
-            head += removeCount
-            // Periodically compact to reclaim memory
-            if head > entries.count / 2 {
-                entries.removeFirst(head)
-                head = 0
-            }
+        let activeCount = entries.count - head
+        guard activeCount > maxCount else { return }
+
+        // Remove down to 75% of maxCount for better amortization
+        let targetCount = (maxCount * 3) / 4
+        let removeCount = activeCount - targetCount
+
+        for i in head..<(head + removeCount) {
+            lookup.removeValue(forKey: entries[i].id)
+        }
+        head += removeCount
+
+        // Compact when head exceeds half the array to reclaim memory
+        if head > entries.count / 2 {
+            entries.removeFirst(head)
+            head = 0
         }
     }
 
@@ -114,24 +120,25 @@ final class MessageDeduplicator {
         lookup.removeAll()
     }
 
-    /// Periodic cleanup
+    /// Periodic cleanup of expired entries and memory optimization.
     func cleanup() {
         lock.lock()
         defer { lock.unlock() }
 
-        cleanupOldEntries()
+        cleanupOldEntries(before: Date().addingTimeInterval(-maxAge))
 
-        if entries.capacity > maxCount * 2 {
+        // Shrink capacity if significantly oversized
+        if entries.capacity > maxCount * 2 && entries.count < maxCount {
             entries.reserveCapacity(maxCount)
         }
     }
 
-    private func cleanupOldEntries() {
-        let cutoff = Date().addingTimeInterval(-maxAge)
+    private func cleanupOldEntries(before cutoff: Date) {
         while head < entries.count, entries[head].timestamp < cutoff {
             lookup.removeValue(forKey: entries[head].id)
             head += 1
         }
+        // Compact when head exceeds half the array
         if head > 0 && head > entries.count / 2 {
             entries.removeFirst(head)
             head = 0

bitchat/_PreviewHelpers/PreviewKeychainManager.swift

@@ -10,32 +10,51 @@ import Foundation
 
 final class PreviewKeychainManager: KeychainManagerProtocol {
     private var storage: [String: Data] = [:]
+    private var serviceStorage: [String: [String: Data]] = [:]
     init() {}
-    
+
     func saveIdentityKey(_ keyData: Data, forKey key: String) -> Bool {
         storage[key] = keyData
         return true
     }
-    
+
     func getIdentityKey(forKey key: String) -> Data? {
         storage[key]
     }
-    
+
     func deleteIdentityKey(forKey key: String) -> Bool {
         storage.removeValue(forKey: key)
         return true
     }
-    
+
     func deleteAllKeychainData() -> Bool {
         storage.removeAll()
+        serviceStorage.removeAll()
         return true
     }
-    
+
     func secureClear(_ data: inout Data) {}
-    
+
     func secureClear(_ string: inout String) {}
-    
+
     func verifyIdentityKeyExists() -> Bool {
         storage["identity_noiseStaticKey"] != nil
     }
+
+    // MARK: - Generic Data Storage (consolidated from KeychainHelper)
+
+    func save(key: String, data: Data, service: String, accessible: CFString?) {
+        if serviceStorage[service] == nil {
+            serviceStorage[service] = [:]
+        }
+        serviceStorage[service]?[key] = data
+    }
+
+    func load(key: String, service: String) -> Data? {
+        serviceStorage[service]?[key]
+    }
+
+    func delete(key: String, service: String) {
+        serviceStorage[service]?.removeValue(forKey: key)
+    }
 }

bitchatTests/Fragmentation/FragmentationTests.swift

@@ -32,29 +32,28 @@ struct FragmentationTests {
         )
         let capture = CaptureDelegate()
         ble.delegate = capture
-        
+
         // Construct a big packet (3KB) from a remote sender (not our own ID)
         let remoteShortID = PeerID(str: "1122334455667788")
         let original = makeLargePublicPacket(senderShortHex: remoteShortID, size: 3_000)
-        
+
         // Use a small fragment size to ensure multiple pieces
         let fragments = fragmentPacket(original, fragmentSize: 400)
-        
+
         // Shuffle fragments to simulate out-of-order arrival
         let shuffled = fragments.shuffled()
-        
-        // Inject fragments spaced out to avoid concurrent mutation inside BLEService
+
+        // Send fragments sequentially with small delays (no fire-and-forget Tasks)
         for (i, fragment) in shuffled.enumerated() {
-            let delay = 5 * Double(i) * 0.001
-            Task {
-                try await sleep(delay)
-                ble._test_handlePacket(fragment, fromPeerID: remoteShortID)
+            if i > 0 {
+                try await Task.sleep(for: .milliseconds(5))
             }
+            ble._test_handlePacket(fragment, fromPeerID: remoteShortID)
         }
-        
-        // Allow async processing
-        try await sleep(0.5)
-        
+
+        // Wait for delegate callback with proper timeout
+        try await capture.waitForPublicMessages(count: 1, timeout: .seconds(2))
+
         #expect(capture.publicMessages.count == 1)
         #expect(capture.publicMessages.first?.content.count == 3_000)
     }
@@ -68,26 +67,26 @@ struct FragmentationTests {
         )
         let capture = CaptureDelegate()
         ble.delegate = capture
-        
+
         let remoteShortID = PeerID(str: "A1B2C3D4E5F60708")
         let original = makeLargePublicPacket(senderShortHex: remoteShortID, size: 2048)
         var frags = fragmentPacket(original, fragmentSize: 300)
-        
+
         // Duplicate one fragment
         if let dup = frags.first {
             frags.insert(dup, at: 1)
         }
-        
+
+        // Send fragments sequentially with small delays (no fire-and-forget Tasks)
         for (i, fragment) in frags.enumerated() {
-            let delay = 5 * Double(i) * 0.001
-            Task {
-                try await sleep(delay)
-                ble._test_handlePacket(fragment, fromPeerID: remoteShortID)
+            if i > 0 {
+                try await Task.sleep(for: .milliseconds(5))
             }
+            ble._test_handlePacket(fragment, fromPeerID: remoteShortID)
         }
-        
-        // Allow async processing
-        try await sleep(0.5)
+
+        // Wait for delegate callback with proper timeout
+        try await capture.waitForPublicMessages(count: 1, timeout: .seconds(2))
 
         #expect(capture.publicMessages.count == 1)
         #expect(capture.publicMessages.first?.content.count == 2048)
@@ -196,12 +195,128 @@ struct FragmentationTests {
 }
 
 extension FragmentationTests {
-    private final class CaptureDelegate: BitchatDelegate {
-        var publicMessages: [(peerID: PeerID, nickname: String, content: String)] = []
-        var receivedMessages: [BitchatMessage] = []
-        func didReceiveMessage(_ message: BitchatMessage) {
-            receivedMessages.append(message)
+    /// Thread-safe delegate that supports awaiting message delivery
+    private final class CaptureDelegate: BitchatDelegate, @unchecked Sendable {
+        private let lock = NSLock()
+        private var _publicMessages: [(peerID: PeerID, nickname: String, content: String)] = []
+        private var _receivedMessages: [BitchatMessage] = []
+        private var publicMessageContinuation: CheckedContinuation<Void, Never>?
+        private var receivedMessageContinuation: CheckedContinuation<Void, Never>?
+        private var expectedPublicMessageCount: Int = 0
+        private var expectedReceivedMessageCount: Int = 0
+
+        var publicMessages: [(peerID: PeerID, nickname: String, content: String)] {
+            lock.lock()
+            defer { lock.unlock() }
+            return _publicMessages
         }
+
+        var receivedMessages: [BitchatMessage] {
+            lock.lock()
+            defer { lock.unlock() }
+            return _receivedMessages
+        }
+
+        func didReceiveMessage(_ message: BitchatMessage) {
+            lock.lock()
+            _receivedMessages.append(message)
+            let count = _receivedMessages.count
+            let expected = expectedReceivedMessageCount
+            let continuation = receivedMessageContinuation
+            lock.unlock()
+
+            if count >= expected, let cont = continuation {
+                lock.lock()
+                receivedMessageContinuation = nil
+                lock.unlock()
+                cont.resume()
+            }
+        }
+
+        func didReceivePublicMessage(from peerID: PeerID, nickname: String, content: String, timestamp: Date, messageID: String?) {
+            lock.lock()
+            _publicMessages.append((peerID, nickname, content))
+            let count = _publicMessages.count
+            let expected = expectedPublicMessageCount
+            let continuation = publicMessageContinuation
+            lock.unlock()
+
+            if count >= expected, let cont = continuation {
+                lock.lock()
+                publicMessageContinuation = nil
+                lock.unlock()
+                cont.resume()
+            }
+        }
+
+        /// Waits for the specified number of public messages to be received
+        func waitForPublicMessages(count: Int, timeout: Duration = .seconds(2)) async throws {
+            lock.lock()
+            if _publicMessages.count >= count {
+                lock.unlock()
+                return
+            }
+            expectedPublicMessageCount = count
+            lock.unlock()
+
+            try await withThrowingTaskGroup(of: Void.self) { group in
+                group.addTask {
+                    await withCheckedContinuation { continuation in
+                        self.lock.lock()
+                        // Recheck count after acquiring lock to avoid race condition
+                        // where message arrives between initial check and continuation install
+                        if self._publicMessages.count >= count {
+                            self.lock.unlock()
+                            continuation.resume()
+                            return
+                        }
+                        self.publicMessageContinuation = continuation
+                        self.lock.unlock()
+                    }
+                }
+                group.addTask {
+                    try await Task.sleep(for: timeout)
+                    throw CancellationError()
+                }
+                try await group.next()
+                group.cancelAll()
+            }
+        }
+
+        /// Waits for the specified number of received messages
+        func waitForReceivedMessages(count: Int, timeout: Duration = .seconds(2)) async throws {
+            lock.lock()
+            if _receivedMessages.count >= count {
+                lock.unlock()
+                return
+            }
+            expectedReceivedMessageCount = count
+            lock.unlock()
+
+            try await withThrowingTaskGroup(of: Void.self) { group in
+                group.addTask {
+                    await withCheckedContinuation { continuation in
+                        self.lock.lock()
+                        // Recheck count after acquiring lock to avoid race condition
+                        // where message arrives between initial check and continuation install
+                        if self._receivedMessages.count >= count {
+                            self.lock.unlock()
+                            continuation.resume()
+                            return
+                        }
+                        self.receivedMessageContinuation = continuation
+                        self.lock.unlock()
+                    }
+                }
+                group.addTask {
+                    try await Task.sleep(for: timeout)
+                    throw CancellationError()
+                }
+                try await group.next()
+                group.cancelAll()
+            }
+        }
+
         func didConnectToPeer(_ peerID: PeerID) {}
         func didDisconnectFromPeer(_ peerID: PeerID) {}
         func didUpdatePeerList(_ peers: [PeerID]) {}
@@ -209,9 +324,6 @@ extension FragmentationTests {
         func didUpdateMessageDeliveryStatus(_ messageID: String, status: DeliveryStatus) {}
         func didReceiveNoisePayload(from peerID: PeerID, type: NoisePayloadType, payload: Data, timestamp: Date) {}
         func didUpdateBluetoothState(_ state: CBManagerState) {}
-        func didReceivePublicMessage(from peerID: PeerID, nickname: String, content: String, timestamp: Date, messageID: String?) {
-            publicMessages.append((peerID, nickname, content))
-        }
         func didReceiveRegionalPublicMessage(from peerID: PeerID, nickname: String, content: String, timestamp: Date) {}
     }
 

bitchatTests/MessageDeduplicationServiceTests.swift

@@ -12,6 +12,8 @@ import Foundation
 
 // MARK: - LRU Deduplication Cache Tests
 
+@Suite("LRU Deduplication Cache")
+@MainActor
 struct LRUDeduplicationCacheTests {
 
     // MARK: - Basic Operations
@@ -265,6 +267,8 @@ struct ContentNormalizerTests {
 
 // MARK: - Message Deduplication Service Tests
 
+@Suite("Message Deduplication Service")
+@MainActor
 struct MessageDeduplicationServiceTests {
 
     // MARK: - Content Deduplication
@@ -467,4 +471,134 @@ struct MessageDeduplicationServiceTests {
         #expect(service.contentTimestamp(for: "hello world") == now)
         #expect(service.contentTimestamp(for: "Hello World") == now)
     }
+
+    // MARK: - Thread Safety Tests (via @MainActor enforcement)
+
+    @Test("Concurrent content recording is safe via MainActor")
+    func concurrentContentRecording() async {
+        let service = MessageDeduplicationService(contentCapacity: 1000, nostrEventCapacity: 1000)
+        let iterations = 100
+
+        // All operations run on MainActor due to @MainActor annotation
+        // This test verifies the pattern works correctly
+        await withTaskGroup(of: Void.self) { group in
+            for i in 0..<iterations {
+                group.addTask { @MainActor in
+                    service.recordContent("Message \(i)", timestamp: Date())
+                }
+            }
+        }
+
+        // Verify some entries were recorded
+        #expect(service.contentTimestamp(for: "Message 0") != nil)
+        #expect(service.contentTimestamp(for: "Message 99") != nil)
+    }
+
+    @Test("Concurrent Nostr event recording is safe via MainActor")
+    func concurrentNostrEventRecording() async {
+        let service = MessageDeduplicationService(contentCapacity: 1000, nostrEventCapacity: 1000)
+        let iterations = 100
+
+        await withTaskGroup(of: Void.self) { group in
+            for i in 0..<iterations {
+                group.addTask { @MainActor in
+                    service.recordNostrEvent("event_\(i)")
+                }
+            }
+        }
+
+        // Verify events were recorded
+        #expect(service.hasProcessedNostrEvent("event_0"))
+        #expect(service.hasProcessedNostrEvent("event_99"))
+    }
+
+    @Test("Mixed concurrent operations are safe via MainActor")
+    func concurrentMixedOperations() async {
+        let service = MessageDeduplicationService(contentCapacity: 1000, nostrEventCapacity: 1000)
+        let iterations = 50
+
+        await withTaskGroup(of: Void.self) { group in
+            // Content recording tasks
+            for i in 0..<iterations {
+                group.addTask { @MainActor in
+                    service.recordContent("Content \(i)", timestamp: Date())
+                }
+            }
+
+            // Event recording tasks
+            for i in 0..<iterations {
+                group.addTask { @MainActor in
+                    service.recordNostrEvent("event_\(i)")
+                }
+            }
+
+            // ACK recording tasks
+            for i in 0..<iterations {
+                group.addTask { @MainActor in
+                    service.recordNostrAck("ack_\(i)")
+                }
+            }
+
+            // Read tasks
+            for i in 0..<iterations {
+                group.addTask { @MainActor in
+                    _ = service.contentTimestamp(for: "Content \(i)")
+                    _ = service.hasProcessedNostrEvent("event_\(i)")
+                    _ = service.hasProcessedNostrAck("ack_\(i)")
+                }
+            }
+        }
+
+        // If we reach here without crashes, the test passes
+    }
+}
+
+// MARK: - LRU Cache Thread Safety Tests
+
+@Suite("LRU Cache Thread Safety")
+@MainActor
+struct LRUCacheThreadSafetyTests {
+
+    @Test("Concurrent cache access is safe via MainActor")
+    func concurrentCacheAccess() async {
+        let cache = LRUDeduplicationCache<Int>(capacity: 500)
+        let iterations = 100
+
+        await withTaskGroup(of: Void.self) { group in
+            // Write tasks
+            for i in 0..<iterations {
+                group.addTask { @MainActor in
+                    cache.record("key_\(i)", value: i)
+                }
+            }
+
+            // Read tasks
+            for i in 0..<iterations {
+                group.addTask { @MainActor in
+                    _ = cache.contains("key_\(i)")
+                    _ = cache.value(for: "key_\(i)")
+                }
+            }
+        }
+
+        // Verify cache is in consistent state
+        #expect(cache.count <= 500) // Respects capacity
+    }
+
+    @Test("Cache eviction under concurrent load is safe")
+    func cacheEvictionUnderLoad() async {
+        let cache = LRUDeduplicationCache<Int>(capacity: 10)
+        let iterations = 100
+
+        await withTaskGroup(of: Void.self) { group in
+            for i in 0..<iterations {
+                group.addTask { @MainActor in
+                    cache.record("key_\(i)", value: i)
+                }
+            }
+        }
+
+        // Cache should maintain its capacity constraint
+        #expect(cache.count == 10)
+    }
 }

bitchatTests/Mocks/MockKeychain.swift

@@ -11,54 +11,144 @@ import Foundation
 
 final class MockKeychain: KeychainManagerProtocol {
     private var storage: [String: Data] = [:]
-    
+    private var serviceStorage: [String: [String: Data]] = [:]
+
     func saveIdentityKey(_ keyData: Data, forKey key: String) -> Bool {
         storage[key] = keyData
         return true
     }
-    
+
     func getIdentityKey(forKey key: String) -> Data? {
         storage[key]
     }
-    
+
     func deleteIdentityKey(forKey key: String) -> Bool {
         storage.removeValue(forKey: key)
         return true
     }
-    
+
     func deleteAllKeychainData() -> Bool {
         storage.removeAll()
+        serviceStorage.removeAll()
         return true
     }
-    
+
     func secureClear(_ data: inout Data) {
-        //
         data = Data()
     }
-    
+
     func secureClear(_ string: inout String) {
         string = ""
     }
-    
+
     func verifyIdentityKeyExists() -> Bool {
         storage["identity_noiseStaticKey"] != nil
     }
+
+    // MARK: - Generic Data Storage (consolidated from KeychainHelper)
+
+    func save(key: String, data: Data, service: String, accessible: CFString?) {
+        if serviceStorage[service] == nil {
+            serviceStorage[service] = [:]
+        }
+        serviceStorage[service]?[key] = data
+    }
+
+    func load(key: String, service: String) -> Data? {
+        serviceStorage[service]?[key]
+    }
+
+    func delete(key: String, service: String) {
+        serviceStorage[service]?.removeValue(forKey: key)
+    }
 }
 
-final class MockKeychainHelper: KeychainHelperProtocol {
-    private typealias Service = String
-    private typealias Key = String
-    private var storage: [Service: [Key: Data]] = [:]
-    
+/// Typealias for backwards compatibility with tests using MockKeychainHelper
+typealias MockKeychainHelper = MockKeychain
+
+/// Mock keychain that tracks secureClear calls for testing DH secret clearing
+final class TrackingMockKeychain: KeychainManagerProtocol {
+    private var storage: [String: Data] = [:]
+    private var serviceStorage: [String: [String: Data]] = [:]
+
+    /// Thread-safe counter for secureClear calls
+    private let lock = NSLock()
+    private var _secureClearDataCallCount = 0
+    private var _secureClearStringCallCount = 0
+
+    var secureClearDataCallCount: Int {
+        lock.lock()
+        defer { lock.unlock() }
+        return _secureClearDataCallCount
+    }
+
+    var secureClearStringCallCount: Int {
+        lock.lock()
+        defer { lock.unlock() }
+        return _secureClearStringCallCount
+    }
+
+    var totalSecureClearCallCount: Int {
+        return secureClearDataCallCount + secureClearStringCallCount
+    }
+
+    func resetCounts() {
+        lock.lock()
+        defer { lock.unlock() }
+        _secureClearDataCallCount = 0
+        _secureClearStringCallCount = 0
+    }
+
+    func saveIdentityKey(_ keyData: Data, forKey key: String) -> Bool {
+        storage[key] = keyData
+        return true
+    }
+
+    func getIdentityKey(forKey key: String) -> Data? {
+        storage[key]
+    }
+
+    func deleteIdentityKey(forKey key: String) -> Bool {
+        storage.removeValue(forKey: key)
+        return true
+    }
+
+    func deleteAllKeychainData() -> Bool {
+        storage.removeAll()
+        serviceStorage.removeAll()
+        return true
+    }
+
+    func secureClear(_ data: inout Data) {
+        lock.lock()
+        _secureClearDataCallCount += 1
+        lock.unlock()
+        data = Data()
+    }
+
+    func secureClear(_ string: inout String) {
+        lock.lock()
+        _secureClearStringCallCount += 1
+        lock.unlock()
+        string = ""
+    }
+
+    func verifyIdentityKeyExists() -> Bool {
+        storage["identity_noiseStaticKey"] != nil
+    }
+
     func save(key: String, data: Data, service: String, accessible: CFString?) {
-        storage[service]?[key] = data
+        if serviceStorage[service] == nil {
+            serviceStorage[service] = [:]
+        }
+        serviceStorage[service]?[key] = data
     }
-    
+
     func load(key: String, service: String) -> Data? {
-        storage[service]?[key]
+        serviceStorage[service]?[key]
     }
-    
+
     func delete(key: String, service: String) {
-        storage[service]?.removeValue(forKey: key)
+        serviceStorage[service]?.removeValue(forKey: key)
     }
 }

bitchatTests/Noise/NoiseProtocolTests.swift

@@ -789,4 +789,159 @@ struct NoiseProtocolTests {
                 "Message \(index + 1): Decrypted payload should match original")
         }
     }
+
+    // MARK: - DH Shared Secret Clearing Tests
+
+    @Test func secureClearCalledDuringHandshake() throws {
+        // Use TrackingMockKeychain to verify secureClear is called
+        let trackingKeychain = TrackingMockKeychain()
+
+        let aliceKey = Curve25519.KeyAgreement.PrivateKey()
+        let bobKey = Curve25519.KeyAgreement.PrivateKey()
+
+        let alice = NoiseSession(
+            peerID: PeerID(str: "alice-test"),
+            role: .initiator,
+            keychain: trackingKeychain,
+            localStaticKey: aliceKey
+        )
+
+        let bob = NoiseSession(
+            peerID: PeerID(str: "bob-test"),
+            role: .responder,
+            keychain: trackingKeychain,
+            localStaticKey: bobKey
+        )
+
+        // Perform handshake
+        let msg1 = try alice.startHandshake()
+        let msg2 = try bob.processHandshakeMessage(msg1)!
+        let msg3 = try alice.processHandshakeMessage(msg2)!
+        _ = try bob.processHandshakeMessage(msg3)
+
+        // In Noise XX pattern handshake:
+        // - Message 1 (initiator): e token only (no DH)
+        // - Message 2 (responder): e, ee, s, es tokens (2 DH operations: ee, es)
+        // - Message 3 (initiator): s, se tokens (1 DH operation: se)
+        // Total in writeMessage: 3 DH operations (ee, es, se)
+        //
+        // In readMessage (performDHOperation):
+        // - After msg1: no DH
+        // - After msg2: ee, es (2 DH operations)
+        // - After msg3: se (1 DH operation)
+        // Total in performDHOperation: 3 DH operations
+        //
+        // Grand total: 6 DH operations requiring secureClear
+        //
+        // Note: .ss pattern is only used in certain handshake patterns, not XX
+        let expectedMinimumCalls = 6
+        #expect(
+            trackingKeychain.secureClearDataCallCount >= expectedMinimumCalls,
+            "Expected at least \(expectedMinimumCalls) secureClear calls for DH secrets, got \(trackingKeychain.secureClearDataCallCount)"
+        )
+    }
+
+    @Test func encryptionWorksAfterSecureClear() throws {
+        // Verify that encryption/decryption still works correctly after adding secureClear
+        let trackingKeychain = TrackingMockKeychain()
+
+        let aliceKey = Curve25519.KeyAgreement.PrivateKey()
+        let bobKey = Curve25519.KeyAgreement.PrivateKey()
+
+        let alice = NoiseSession(
+            peerID: PeerID(str: "alice-test-enc"),
+            role: .initiator,
+            keychain: trackingKeychain,
+            localStaticKey: aliceKey
+        )
+
+        let bob = NoiseSession(
+            peerID: PeerID(str: "bob-test-enc"),
+            role: .responder,
+            keychain: trackingKeychain,
+            localStaticKey: bobKey
+        )
+
+        // Perform handshake
+        let msg1 = try alice.startHandshake()
+        let msg2 = try bob.processHandshakeMessage(msg1)!
+        let msg3 = try alice.processHandshakeMessage(msg2)!
+        _ = try bob.processHandshakeMessage(msg3)
+
+        // Verify both sessions are established
+        #expect(alice.isEstablished())
+        #expect(bob.isEstablished())
+
+        // Verify secureClear was called (basic sanity check)
+        #expect(trackingKeychain.secureClearDataCallCount > 0)
+
+        // Test encryption from Alice to Bob
+        let plaintext1 = "Hello from Alice after secureClear!".data(using: .utf8)!
+        let ciphertext1 = try alice.encrypt(plaintext1)
+        let decrypted1 = try bob.decrypt(ciphertext1)
+        #expect(decrypted1 == plaintext1)
+
+        // Test encryption from Bob to Alice
+        let plaintext2 = "Hello from Bob after secureClear!".data(using: .utf8)!
+        let ciphertext2 = try bob.encrypt(plaintext2)
+        let decrypted2 = try alice.decrypt(ciphertext2)
+        #expect(decrypted2 == plaintext2)
+
+        // Test multiple messages to verify cipher state is correct
+        for i in 1...10 {
+            let msg = "Message \(i) from Alice".data(using: .utf8)!
+            let cipher = try alice.encrypt(msg)
+            let dec = try bob.decrypt(cipher)
+            #expect(dec == msg)
+        }
+    }
+
+    @Test func secureClearCalledInBothWriteAndReadPaths() throws {
+        // Verify secureClear is called in both writeMessage and readMessage paths
+        // We do this by checking the count increases at each step
+
+        let aliceKeychain = TrackingMockKeychain()
+        let bobKeychain = TrackingMockKeychain()
+
+        let aliceKey = Curve25519.KeyAgreement.PrivateKey()
+        let bobKey = Curve25519.KeyAgreement.PrivateKey()
+
+        let alice = NoiseSession(
+            peerID: PeerID(str: "alice-paths"),
+            role: .initiator,
+            keychain: aliceKeychain,
+            localStaticKey: aliceKey
+        )
+
+        let bob = NoiseSession(
+            peerID: PeerID(str: "bob-paths"),
+            role: .responder,
+            keychain: bobKeychain,
+            localStaticKey: bobKey
+        )
+
+        // Message 1: Alice writes (e token only, no DH)
+        let msg1 = try alice.startHandshake()
+        let aliceCountAfterMsg1 = aliceKeychain.secureClearDataCallCount
+        // No DH in message 1 for initiator
+        #expect(aliceCountAfterMsg1 == 0, "No DH secrets in message 1 write")
+
+        // Bob reads message 1 (no DH) and writes message 2 (ee, es DH operations)
+        let msg2 = try bob.processHandshakeMessage(msg1)!
+        let bobCountAfterMsg2 = bobKeychain.secureClearDataCallCount
+        // Bob should have cleared secrets for: ee (read), es (read), ee (write), es (write)
+        #expect(bobCountAfterMsg2 >= 2, "Bob should clear DH secrets when processing/writing message 2")
+
+        // Alice reads message 2 (ee, es) and writes message 3 (se)
+        let msg3 = try alice.processHandshakeMessage(msg2)!
+        let aliceCountAfterMsg3 = aliceKeychain.secureClearDataCallCount
+        // Alice should have cleared: ee (read), es (read), se (write)
+        #expect(aliceCountAfterMsg3 >= 3, "Alice should clear DH secrets when processing/writing message 3")
+
+        // Bob reads message 3 (se)
+        _ = try bob.processHandshakeMessage(msg3)
+        let bobFinalCount = bobKeychain.secureClearDataCallCount
+        // Bob should have additionally cleared: se (read)
+        #expect(bobFinalCount > bobCountAfterMsg2, "Bob should clear DH secrets when processing message 3")
+    }
 }

bitchatTests/Services/NostrTransportTests.swift

@@ -0,0 +1,108 @@
+//
+// NostrTransportTests.swift
+// bitchat
+//
+// This is free and unencumbered software released into the public domain.
+// For more information, see <https://unlicense.org>
+//
+
+import Foundation
+import Testing
+@testable import bitchat
+
+@Suite("NostrTransport Thread Safety Tests")
+struct NostrTransportTests {
+
+    @Test("Concurrent read receipt enqueue does not crash")
+    @MainActor
+    func concurrentReadReceiptEnqueue() async throws {
+        let keychain = MockKeychain()
+        let idBridge = NostrIdentityBridge(keychain: keychain)
+        let transport = NostrTransport(keychain: keychain, idBridge: idBridge)
+
+        // Create 100 concurrent read receipt submissions
+        let iterations = 100
+
+        await withTaskGroup(of: Void.self) { group in
+            for i in 0..<iterations {
+                group.addTask {
+                    let receipt = ReadReceipt(
+                        originalMessageID: UUID().uuidString,
+                        readerID: PeerID(str: String(format: "%016x", i)),
+                        readerNickname: "Reader\(i)"
+                    )
+                    let peerID = PeerID(str: String(format: "%016x", i))
+                    transport.sendReadReceipt(receipt, to: peerID)
+                }
+            }
+        }
+
+        // If we reach here without crashing, the test passes
+        // The concurrent enqueue operations completed without data races
+    }
+
+    @Test("Read queue processes under concurrent load")
+    @MainActor
+    func readQueueProcessingUnderLoad() async throws {
+        let keychain = MockKeychain()
+        let idBridge = NostrIdentityBridge(keychain: keychain)
+        let transport = NostrTransport(keychain: keychain, idBridge: idBridge)
+
+        // Rapidly enqueue many receipts from multiple concurrent sources
+        let iterations = 50
+
+        // First batch - rapid fire
+        for i in 0..<iterations {
+            let receipt = ReadReceipt(
+                originalMessageID: UUID().uuidString,
+                readerID: PeerID(str: String(format: "%016x", i)),
+                readerNickname: "Reader\(i)"
+            )
+            transport.sendReadReceipt(receipt, to: PeerID(str: String(format: "%016x", i)))
+        }
+
+        // Give some time for processing to start
+        try await Task.sleep(nanoseconds: 100_000_000) // 100ms
+
+        // Second batch - while first might be processing
+        await withTaskGroup(of: Void.self) { group in
+            for i in iterations..<(iterations * 2) {
+                group.addTask {
+                    let receipt = ReadReceipt(
+                        originalMessageID: UUID().uuidString,
+                        readerID: PeerID(str: String(format: "%016x", i)),
+                        readerNickname: "Reader\(i)"
+                    )
+                    transport.sendReadReceipt(receipt, to: PeerID(str: String(format: "%016x", i)))
+                }
+            }
+        }
+
+        // If we reach here without crashing or deadlocking, test passes
+    }
+
+    @Test("isPeerReachable is thread safe")
+    @MainActor
+    func isPeerReachableThreadSafety() async throws {
+        let keychain = MockKeychain()
+        let idBridge = NostrIdentityBridge(keychain: keychain)
+        let transport = NostrTransport(keychain: keychain, idBridge: idBridge)
+
+        let iterations = 100
+
+        // Concurrent reads on isPeerReachable
+        await withTaskGroup(of: Bool.self) { group in
+            for i in 0..<iterations {
+                group.addTask {
+                    let peerID = PeerID(str: String(format: "%016x", i))
+                    return transport.isPeerReachable(peerID)
+                }
+            }
+
+            // Collect results (all should be false since no favorites configured)
+            for await result in group {
+                #expect(result == false)
+            }
+        }
+    }
+}

bitchatTests/Utils/HexStringTests.swift

@@ -0,0 +1,108 @@
+//
+// HexStringTests.swift
+// bitchatTests
+//
+// Tests for Data(hexString:) hex parsing
+//
+
+import Testing
+import Foundation
+@testable import bitchat
+
+struct HexStringTests {
+
+    // MARK: - Valid Hex Strings
+
+    @Test func validHexString() {
+        let data = Data(hexString: "0102030405")
+        #expect(data == Data([0x01, 0x02, 0x03, 0x04, 0x05]))
+    }
+
+    @Test func validHexStringUppercase() {
+        let data = Data(hexString: "AABBCCDD")
+        #expect(data == Data([0xAA, 0xBB, 0xCC, 0xDD]))
+    }
+
+    @Test func validHexStringMixedCase() {
+        let data = Data(hexString: "aAbBcCdD")
+        #expect(data == Data([0xAA, 0xBB, 0xCC, 0xDD]))
+    }
+
+    @Test func validHexStringWith0xPrefix() {
+        let data = Data(hexString: "0x0102030405")
+        #expect(data == Data([0x01, 0x02, 0x03, 0x04, 0x05]))
+    }
+
+    @Test func validHexStringWith0XPrefix() {
+        let data = Data(hexString: "0XAABBCCDD")
+        #expect(data == Data([0xAA, 0xBB, 0xCC, 0xDD]))
+    }
+
+    @Test func validHexStringWithWhitespace() {
+        let data = Data(hexString: "  0102030405  ")
+        #expect(data == Data([0x01, 0x02, 0x03, 0x04, 0x05]))
+    }
+
+    @Test func validHexStringWith0xPrefixAndWhitespace() {
+        let data = Data(hexString: "  0x0102030405  ")
+        #expect(data == Data([0x01, 0x02, 0x03, 0x04, 0x05]))
+    }
+
+    @Test func emptyHexString() {
+        let data = Data(hexString: "")
+        #expect(data == Data())
+    }
+
+    @Test func emptyHexStringWithWhitespace() {
+        let data = Data(hexString: "   ")
+        #expect(data == Data())
+    }
+
+    @Test func emptyHexStringWith0xPrefix() {
+        let data = Data(hexString: "0x")
+        #expect(data == Data())
+    }
+
+    // MARK: - Invalid Hex Strings
+
+    @Test func oddLengthHexStringReturnsNil() {
+        let data = Data(hexString: "012")
+        #expect(data == nil)
+    }
+
+    @Test func oddLengthHexStringWith0xPrefixReturnsNil() {
+        let data = Data(hexString: "0x012")
+        #expect(data == nil)
+    }
+
+    @Test func invalidCharactersReturnNil() {
+        let data = Data(hexString: "GHIJ")
+        #expect(data == nil)
+    }
+
+    @Test func mixedValidAndInvalidCharactersReturnNil() {
+        let data = Data(hexString: "01GH")
+        #expect(data == nil)
+    }
+
+    @Test func specialCharactersReturnNil() {
+        let data = Data(hexString: "01-02")
+        #expect(data == nil)
+    }
+
+    // MARK: - Round Trip Tests
+
+    @Test func roundTripConversion() {
+        let original = Data([0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88, 0x99, 0xAA, 0xBB, 0xCC, 0xDD, 0xEE, 0xFF])
+        let hexString = original.hexEncodedString()
+        let roundTripped = Data(hexString: hexString)
+        #expect(roundTripped == original)
+    }
+
+    @Test func roundTripConversionWith0xPrefix() {
+        let original = Data([0xDE, 0xAD, 0xBE, 0xEF])
+        let hexString = "0x" + original.hexEncodedString()
+        let roundTripped = Data(hexString: hexString)
+        #expect(roundTripped == original)
+    }
+}