diff --git a/CLAUDE.md b/CLAUDE.md
index 1b585c8..0213898 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -23,6 +23,7 @@ For Flutter/Dart code:
 - `cd backend && ./run.sh` from the `backend/` folder - Run the backend
 - `cd frontend && ./run.sh` from the `frontend/` folder - Run the front-end for the web
 - `cd backend && ./run_tests.sh` - Run the backend tests
+- `cd frontend && ./run_tests.sh` - Run the front-end tests
 - `cd backend && ./lint.sh` - Run the clippy linter for Rust code
 - `dart analyze` - Run the Dart linter
 - `cd backend/data && ./update_mac_vendors --llm` - Update the MAC vendors list from the web and re-calculate the vedors -> device type list
@@ -49,7 +50,8 @@ For Flutter/Dart code:
 ## Important notes
 - NEVER add or commit .env files or files with secrets (passwords, API keys or similar information)
 - Code must be as simple as possible, human readable and modularized
-- ALWAYS write unit tests for new or modified backend components
+- ALWAYS write and/or update unit tests for new or modified backend components
+- ALWAYS write and/or update unit, API and widget tests for new or modified frontend components
 - ALWAYS run all tests after making a new change and do not continue until all tests pass
 - When adding a new API endpoint, ALWAYS wire it to the OpenAPI generation
 - When adding a significant chunk of new code (either Rust or Dart), run the corresponding linter
diff --git a/TODO.md b/TODO.md
index 710878b..84e9353 100644
--- a/TODO.md
+++ b/TODO.md
@@ -17,7 +17,7 @@
 
 ## Frontend
 
-- [ ] Can we add front-end tests?
+- [x] Can we add front-end tests?
 - [x] Break down oott_api.dart in modules
 
 ## Improve engine
diff --git a/frontend/lib/utils/backend_reachability.dart b/frontend/lib/utils/backend_reachability.dart
index 3139157..00a92fe 100644
--- a/frontend/lib/utils/backend_reachability.dart
+++ b/frontend/lib/utils/backend_reachability.dart
@@ -38,6 +38,16 @@ class BackendReachability extends ChangeNotifier {
     _prober = prober;
   }
 
+  /// Test-only hook to force a deterministic online state so polling widgets
+  /// load during tests (where connectivity_plus has no platform backing).
+  @visibleForTesting
+  void forceOnlineForTesting() {
+    _deviceHasNetwork = true;
+    _isBackendReachable = true;
+    _lastErrorMessage = null;
+    notifyListeners();
+  }
+
   void recordSuccess() {
     _lastSuccessAt = DateTime.now();
     _lastErrorMessage = null;
diff --git a/frontend/lib/utils/oott_api.dart b/frontend/lib/utils/oott_api.dart
index f2a6539..788a7f2 100644
--- a/frontend/lib/utils/oott_api.dart
+++ b/frontend/lib/utils/oott_api.dart
@@ -2,6 +2,7 @@ library;
 
 import 'package:dio/dio.dart';
 import 'package:encrypter/encrypter/xor.dart';
+import 'package:flutter/foundation.dart';
 
 import 'api/api_error.dart';
 import 'api/dio_config.dart';
@@ -45,6 +46,18 @@ class BackendAPI {
     BackendReachability.instance.setProber(() => _dio.get('/test'));
   }
 
+  /// Test-only access to the underlying [Dio] so tests can swap in a client
+  /// with a mock adapter installed. Mirrors [reconfigureFromPrefs]'s prober
+  /// wiring so reachability stays consistent after a swap.
+  @visibleForTesting
+  Dio get dioForTesting => _dio;
+
+  @visibleForTesting
+  set dioForTesting(Dio dio) {
+    _dio = dio;
+    BackendReachability.instance.setProber(() => _dio.get('/test'));
+  }
+
   // Returns null if the test was successful, and a String with a message about the issue if not
   static Future<String?> test(String baseUrl, String apiKey) async {
     final dio = buildDio(
diff --git a/frontend/pubspec.lock b/frontend/pubspec.lock
index 517259e..b09b40b 100644
--- a/frontend/pubspec.lock
+++ b/frontend/pubspec.lock
@@ -240,6 +240,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.6.0"
+  http_mock_adapter:
+    dependency: "direct dev"
+    description:
+      name: http_mock_adapter
+      sha256: "46399c78bd4a0af071978edd8c502d7aeeed73b5fb9860bca86b5ed647a63c1b"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.6.1"
   http_parser:
     dependency: transitive
     description:
@@ -312,6 +320,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "6.1.0"
+  logger:
+    dependency: transitive
+    description:
+      name: logger
+      sha256: "25aee487596a6257655a1e091ec2ae66bc30e7af663592cc3a27e6591e05035c"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.7.0"
   logging:
     dependency: transitive
     description:
diff --git a/frontend/pubspec.yaml b/frontend/pubspec.yaml
index cfb7dda..fea650d 100644
--- a/frontend/pubspec.yaml
+++ b/frontend/pubspec.yaml
@@ -26,6 +26,7 @@ dev_dependencies:
   flutter_test:
     sdk: flutter
   flutter_lints: ^6.0.0
+  http_mock_adapter: ^0.6.1
 
 flutter:
   uses-material-design: true
diff --git a/frontend/run_tests.sh b/frontend/run_tests.sh
new file mode 100755
index 0000000..c3283a7
--- /dev/null
+++ b/frontend/run_tests.sh
@@ -0,0 +1,2 @@
+#!/bin/sh
+flutter test
diff --git a/frontend/test/api/backend_api_test_endpoint_test.dart b/frontend/test/api/backend_api_test_endpoint_test.dart
new file mode 100644
index 0000000..ae3eed5
--- /dev/null
+++ b/frontend/test/api/backend_api_test_endpoint_test.dart
@@ -0,0 +1,18 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/utils/oott_api.dart';
+
+void main() {
+  // BackendAPI.test() builds its own Dio internally (no injectable seam), so
+  // only its error-mapping path is testable here: an unresolvable host must
+  // come back as a non-null, user-facing message rather than throwing. The
+  // success path is a documented coverage gap.
+  test('BackendAPI.test returns a user message for an unreachable backend',
+      () async {
+    // Loopback port 1 is closed: connection is refused immediately, keeping the
+    // test hermetic (no DNS, no TLS, no traffic leaving the machine).
+    final result = await BackendAPI.test('http://127.0.0.1:1/api', '');
+
+    expect(result, isNotNull);
+    expect(result, isNotEmpty);
+  });
+}
diff --git a/frontend/test/api/devices_api_test.dart b/frontend/test/api/devices_api_test.dart
new file mode 100644
index 0000000..b45a93a
--- /dev/null
+++ b/frontend/test/api/devices_api_test.dart
@@ -0,0 +1,182 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/model/device_type.dart';
+import 'package:frontend/utils/oott_api.dart';
+import 'package:http_mock_adapter/http_mock_adapter.dart';
+
+import '../helpers/backend_test_harness.dart';
+import '../helpers/fixtures.dart';
+
+void main() {
+  late DioAdapter adapter;
+
+  setUp(() async {
+    adapter = await setUpBackendForTest();
+  });
+
+  test('getDevice fetches and decodes a single device', () async {
+    adapter.onGet(
+      '/devices/aa:bb:cc:dd:ee:ff',
+      (server) => server.reply(200, deviceJson(owner: 'carol')),
+    );
+
+    final device = await BackendAPI.instance.getDevice('aa:bb:cc:dd:ee:ff');
+
+    expect(device.owner, 'carol');
+  });
+
+  test('getDeviceSummary GETs /devices/summary', () async {
+    adapter.onGet(
+      '/devices/summary',
+      (server) => server.reply(200, deviceSummaryJson(totalRegistered: 7)),
+    );
+
+    final summary = await BackendAPI.instance.getDeviceSummary();
+
+    expect(summary.totalRegistered, 7);
+  });
+
+  test('listDevices sends filter + pagination params and trims extra item',
+      () async {
+    adapter.onGet(
+      '/devices',
+      (server) => server.reply(200, [
+        deviceJson(macAddress: '00:00:00:00:00:01'),
+        deviceJson(macAddress: '00:00:00:00:00:02'),
+        deviceJson(macAddress: '00:00:00:00:00:03'),
+      ]),
+      queryParameters: {
+        'is_registered': false,
+        'device_type': 'laptop',
+        'sort_by': 'last_seen',
+        'sort_order': 'asc',
+        'page_offset': 0,
+        'page_limit': 3,
+      },
+    );
+
+    final result = await BackendAPI.instance.listDevices(
+      isRegistered: false,
+      deviceType: DeviceType.laptop,
+      sortBy: 'last_seen',
+      sortAscending: true,
+      page: 0,
+      perPage: 2,
+    );
+
+    expect(result.items, hasLength(2));
+    expect(result.hasNextPage, isTrue);
+  });
+
+  test('listDevices reports no next page when fewer than perPage+1 returned',
+      () async {
+    adapter.onGet(
+      '/devices',
+      (server) => server.reply(200, [deviceJson()]),
+    );
+
+    final result = await BackendAPI.instance.listDevices(perPage: 2);
+
+    expect(result.items, hasLength(1));
+    expect(result.hasNextPage, isFalse);
+  });
+
+  test('listDevices maps the unknown device type to an empty filter', () async {
+    adapter.onGet(
+      '/devices',
+      (server) => server.reply(200, <dynamic>[]),
+      queryParameters: {
+        'device_type': '',
+        'page_offset': 0,
+        'page_limit': 11,
+      },
+    );
+
+    final result = await BackendAPI.instance.listDevices(
+      deviceType: DeviceType.unknown,
+    );
+
+    expect(result.items, isEmpty);
+  });
+
+  test('registerDevice PUTs the device payload', () async {
+    adapter.onPut(
+      '/devices',
+      (server) => server.reply(200, null),
+      data: {
+        'mac_address': 'aa:bb:cc:dd:ee:ff',
+        'owner': 'dave',
+        'device_type': 'phone',
+        'name': 'Dave Phone',
+      },
+    );
+
+    await BackendAPI.instance.registerDevice(
+      'aa:bb:cc:dd:ee:ff',
+      'dave',
+      'phone',
+      name: 'Dave Phone',
+    );
+  });
+
+  test('updateDevice PUTs to the device path', () async {
+    adapter.onPut(
+      '/devices/aa:bb:cc:dd:ee:ff',
+      (server) => server.reply(200, null),
+      data: {
+        'owner': 'erin',
+        'device_type': 'tv',
+        'vendor': 'Globex',
+        'name': null,
+      },
+    );
+
+    await BackendAPI.instance.updateDevice(
+      'aa:bb:cc:dd:ee:ff',
+      'erin',
+      'tv',
+      'Globex',
+    );
+  });
+
+  test('forgetDevice DELETEs the device path', () async {
+    adapter.onDelete(
+      '/devices/aa:bb:cc:dd:ee:ff',
+      (server) => server.reply(200, null),
+    );
+
+    await BackendAPI.instance.forgetDevice('aa:bb:cc:dd:ee:ff');
+  });
+
+  test('getDeviceEvents decodes a list of events', () async {
+    adapter.onGet(
+      '/devices/aa:bb:cc:dd:ee:ff/events',
+      (server) => server.reply(200, [
+        deviceEventJson(id: 1, scanner: 'Arp'),
+        deviceEventJson(id: 2, scanner: 'Mdns'),
+      ]),
+    );
+
+    final events = await BackendAPI.instance.getDeviceEvents(
+      'aa:bb:cc:dd:ee:ff',
+    );
+
+    expect(events, hasLength(2));
+    expect(events.first.scannerLabel, 'ARP');
+  });
+
+  test('getDeviceEvents sends created_from when provided', () async {
+    final from = DateTime.utc(2026, 5, 1, 0, 0, 0);
+    adapter.onGet(
+      '/devices/aa:bb:cc:dd:ee:ff/events',
+      (server) => server.reply(200, <dynamic>[]),
+      queryParameters: {'created_from': from.toIso8601String()},
+    );
+
+    final events = await BackendAPI.instance.getDeviceEvents(
+      'aa:bb:cc:dd:ee:ff',
+      createdFrom: from,
+    );
+
+    expect(events, isEmpty);
+  });
+}
diff --git a/frontend/test/api/notifications_api_test.dart b/frontend/test/api/notifications_api_test.dart
new file mode 100644
index 0000000..a11987f
--- /dev/null
+++ b/frontend/test/api/notifications_api_test.dart
@@ -0,0 +1,89 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/utils/oott_api.dart';
+import 'package:http_mock_adapter/http_mock_adapter.dart';
+
+import '../helpers/backend_test_harness.dart';
+import '../helpers/fixtures.dart';
+
+void main() {
+  late DioAdapter adapter;
+
+  setUp(() async {
+    adapter = await setUpBackendForTest();
+  });
+
+  test('markNotificationAsRead GETs the notification path', () async {
+    adapter.onGet(
+      '/notifications/7',
+      (server) => server.reply(200, null),
+    );
+
+    await BackendAPI.instance.markNotificationAsRead(7);
+  });
+
+  test('markNotificationAsNew POSTs to mark_as_new', () async {
+    adapter.onPost(
+      '/notifications/7/mark_as_new',
+      (server) => server.reply(200, null),
+    );
+
+    await BackendAPI.instance.markNotificationAsNew(7);
+  });
+
+  test('markAllNotificationsAsRead POSTs to mark_all_as_old', () async {
+    adapter.onPost(
+      '/notifications/mark_all_as_old',
+      (server) => server.reply(200, null),
+    );
+
+    await BackendAPI.instance.markAllNotificationsAsRead();
+  });
+
+  test('listNotifications sends is_new + pagination and trims extra item',
+      () async {
+    adapter.onGet(
+      '/notifications',
+      (server) => server.reply(200, [
+        notificationJson(id: 1),
+        notificationJson(id: 2),
+        notificationJson(id: 3),
+      ]),
+      queryParameters: {
+        'is_new': true,
+        'page_offset': 0,
+        'page_limit': 3,
+      },
+    );
+
+    final result = await BackendAPI.instance.listNotifications(
+      true,
+      page: 0,
+      perPage: 2,
+    );
+
+    expect(result.items, hasLength(2));
+    expect(result.hasNextPage, isTrue);
+  });
+
+  test('listNotifications maps a null filter to an empty is_new param',
+      () async {
+    adapter.onGet(
+      '/notifications',
+      (server) => server.reply(200, <dynamic>[]),
+      queryParameters: {
+        'is_new': '',
+        'page_offset': 10,
+        'page_limit': 6,
+      },
+    );
+
+    final result = await BackendAPI.instance.listNotifications(
+      null,
+      page: 2,
+      perPage: 5,
+    );
+
+    expect(result.items, isEmpty);
+    expect(result.hasNextPage, isFalse);
+  });
+}
diff --git a/frontend/test/api/scanners_api_test.dart b/frontend/test/api/scanners_api_test.dart
new file mode 100644
index 0000000..1be7fb5
--- /dev/null
+++ b/frontend/test/api/scanners_api_test.dart
@@ -0,0 +1,81 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/utils/oott_api.dart';
+import 'package:http_mock_adapter/http_mock_adapter.dart';
+
+import '../helpers/backend_test_harness.dart';
+import '../helpers/fixtures.dart';
+
+void main() {
+  late DioAdapter adapter;
+
+  setUp(() async {
+    adapter = await setUpBackendForTest();
+  });
+
+  test('getArpScannerStatus decodes /arp_scanner/status', () async {
+    adapter.onGet(
+      '/arp_scanner/status',
+      (server) => server.reply(
+        200,
+        intervalScannerJson(isRunning: true, runningForSeconds: 12),
+      ),
+    );
+
+    final status = await BackendAPI.instance.getArpScannerStatus();
+
+    expect(status.isRunning, isTrue);
+    expect(status.runningForSeconds, 12.0);
+  });
+
+  test('getSnmpScannerStatus decodes /snmp_scanner/status', () async {
+    adapter.onGet(
+      '/snmp_scanner/status',
+      (server) => server.reply(200, intervalScannerJson(isRunning: false)),
+    );
+
+    final status = await BackendAPI.instance.getSnmpScannerStatus();
+
+    expect(status.isRunning, isFalse);
+  });
+
+  test('getMdnsScannerStatus decodes /mdns_scanner/status', () async {
+    adapter.onGet(
+      '/mdns_scanner/status',
+      (server) => server.reply(
+        200,
+        listenerScannerJson(isListening: true, devicesSeen: 3),
+      ),
+    );
+
+    final status = await BackendAPI.instance.getMdnsScannerStatus();
+
+    expect(status.isListening, isTrue);
+    expect(status.devicesSeen, 3);
+  });
+
+  test('getSsdpScannerStatus decodes /ssdp_scanner/status', () async {
+    adapter.onGet(
+      '/ssdp_scanner/status',
+      (server) => server.reply(200, listenerScannerJson(devicesSeen: 1)),
+    );
+
+    final status = await BackendAPI.instance.getSsdpScannerStatus();
+
+    expect(status.devicesSeen, 1);
+  });
+
+  test('getDhcpScannerStatus decodes /dhcp_scanner/status', () async {
+    adapter.onGet(
+      '/dhcp_scanner/status',
+      (server) => server.reply(
+        200,
+        listenerScannerJson(isListening: true, devicesSeen: 5),
+      ),
+    );
+
+    final status = await BackendAPI.instance.getDhcpScannerStatus();
+
+    expect(status.isListening, isTrue);
+    expect(status.devicesSeen, 5);
+  });
+}
diff --git a/frontend/test/flutter_test_config.dart b/frontend/test/flutter_test_config.dart
new file mode 100644
index 0000000..e38d86b
--- /dev/null
+++ b/frontend/test/flutter_test_config.dart
@@ -0,0 +1,12 @@
+import 'dart:async';
+
+import 'package:google_fonts/google_fonts.dart';
+
+/// Global test bootstrap, picked up automatically by `flutter test` for every
+/// test under `test/`. Disables Google Fonts runtime fetching so no test can
+/// accidentally hit the network for a font (tests render screens directly
+/// rather than through the app shell, but this is a cheap safety net).
+Future<void> testExecutable(FutureOr<void> Function() testMain) async {
+  GoogleFonts.config.allowRuntimeFetching = false;
+  await testMain();
+}
diff --git a/frontend/test/helpers/backend_test_harness.dart b/frontend/test/helpers/backend_test_harness.dart
new file mode 100644
index 0000000..b2aaae1
--- /dev/null
+++ b/frontend/test/helpers/backend_test_harness.dart
@@ -0,0 +1,67 @@
+import 'package:dio/dio.dart';
+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/utils/backend_reachability.dart';
+import 'package:frontend/utils/oott_api.dart';
+import 'package:frontend/utils/pref_utils.dart';
+import 'package:http_mock_adapter/http_mock_adapter.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+const _connectivityMethodChannel = MethodChannel(
+  'dev.fluttercommunity.plus/connectivity',
+);
+const _connectivityEventChannel = EventChannel(
+  'dev.fluttercommunity.plus/connectivity_status',
+);
+
+bool _channelsStubbed = false;
+
+/// Neutralises the connectivity_plus platform channels so the
+/// [BackendReachability] singleton can be constructed in tests without the
+/// plugin throwing `MissingPluginException`. `check` reports a network, and
+/// the change stream stays open but emits nothing.
+void _stubConnectivityChannels() {
+  if (_channelsStubbed) return;
+  final messenger =
+      TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger;
+  messenger.setMockMethodCallHandler(_connectivityMethodChannel, (call) async {
+    if (call.method == 'check') return <String>['wifi'];
+    return null;
+  });
+  messenger.setMockStreamHandler(
+    _connectivityEventChannel,
+    MockStreamHandler.inline(onListen: (arguments, events) {}),
+  );
+  _channelsStubbed = true;
+}
+
+/// Prepares the backend singletons for a test and returns a [DioAdapter] so the
+/// test can stub HTTP routes. Call from `setUp`.
+///
+/// This (1) seeds mock SharedPreferences, (2) stubs the connectivity channels,
+/// (3) forces [BackendReachability] online so polling widgets load, and
+/// (4) swaps the [BackendAPI] singleton's Dio for one backed by a mock adapter.
+///
+/// `prefs` are only honoured on the first call within a test isolate, because
+/// `PrefUtil` caches the SharedPreferences instance after its one-shot init.
+/// Use [PrefUtil.setValue] for per-test changes after that.
+Future<DioAdapter> setUpBackendForTest({
+  Map<String, Object> prefs = const {},
+}) async {
+  TestWidgetsFlutterBinding.ensureInitialized();
+  _stubConnectivityChannels();
+
+  SharedPreferences.setMockInitialValues({
+    'base_url': 'http://test.local/api',
+    'api_key': '',
+    ...prefs,
+  });
+  await PrefUtil.init();
+
+  BackendReachability.instance.forceOnlineForTesting();
+
+  final dio = Dio(BaseOptions(baseUrl: 'http://test.local/api'));
+  final adapter = DioAdapter(dio: dio);
+  BackendAPI.instance.dioForTesting = dio;
+  return adapter;
+}
diff --git a/frontend/test/helpers/fixtures.dart b/frontend/test/helpers/fixtures.dart
new file mode 100644
index 0000000..fb7f536
--- /dev/null
+++ b/frontend/test/helpers/fixtures.dart
@@ -0,0 +1,103 @@
+/// Typed JSON builders mirroring the backend response shapes, so route stubs
+/// and model tests stay terse and use the exact snake_case keys the app's
+/// `fromJson` constructors read. Every field has a sensible default; override
+/// only what a given test cares about.
+library;
+
+Map<String, dynamic> deviceJson({
+  String macAddress = 'aa:bb:cc:dd:ee:ff',
+  String ipv4Address = '192.168.0.10',
+  String vendor = 'Acme Corp',
+  String lastSeen = '2026-06-01T12:00:00Z',
+  bool isRegistered = false,
+  String owner = 'alice',
+  String deviceType = 'laptop',
+  String? name,
+}) => {
+  'mac_address': macAddress,
+  'ipv4_address': ipv4Address,
+  'vendor': vendor,
+  'last_seen': lastSeen,
+  'is_registered': isRegistered,
+  'owner': owner,
+  'device_type': deviceType,
+  'name': name,
+};
+
+Map<String, dynamic> deviceSummaryJson({
+  int totalRegistered = 0,
+  int seenLastDayRegistered = 0,
+  int seenLastDayUnregistered = 0,
+  int seenLastWeekRegistered = 0,
+  int seenLastWeekUnregistered = 0,
+}) => {
+  'total_registered': totalRegistered,
+  'seen_last_day_registered': seenLastDayRegistered,
+  'seen_last_day_unregistered': seenLastDayUnregistered,
+  'seen_last_week_registered': seenLastWeekRegistered,
+  'seen_last_week_unregistered': seenLastWeekUnregistered,
+};
+
+Map<String, dynamic> deviceEventJson({
+  int id = 1,
+  String macAddress = 'aa:bb:cc:dd:ee:ff',
+  String createdOn = '2026-06-01T12:00:00Z',
+  String eventType = 'seen',
+  String ipv4Address = '192.168.0.10',
+  String vendor = 'Acme Corp',
+  String scanner = 'Arp',
+}) => {
+  'id': id,
+  'mac_address': macAddress,
+  'created_on': createdOn,
+  'event_type': eventType,
+  'ipv4_address': ipv4Address,
+  'vendor': vendor,
+  'scanner': scanner,
+};
+
+Map<String, dynamic> notificationJson({
+  int id = 1,
+  String createdOn = '2026-06-01T12:00:00Z',
+  String notificationType = 'newDeviceFound',
+  String title = 'New device found',
+  String body = 'A new device joined the network',
+  bool isNew = true,
+  String? macAddress = 'aa:bb:cc:dd:ee:ff',
+}) => {
+  'id': id,
+  'created_on': createdOn,
+  'notification_type': notificationType,
+  'title': title,
+  'body': body,
+  'is_new': isNew,
+  'mac_address': macAddress,
+};
+
+/// Shape shared by the ARP and SNMP scanners (run-on-interval scanners).
+Map<String, dynamic> intervalScannerJson({
+  bool isRunning = false,
+  double? runningForSeconds,
+  double? nextRunInSeconds,
+  int? lastScanDevicesSeen,
+  double? lastScanSecondsAgo,
+}) => {
+  'is_running': isRunning,
+  'running_for_seconds': runningForSeconds,
+  'next_run_in_seconds': nextRunInSeconds,
+  'last_scan_devices_seen': lastScanDevicesSeen,
+  'last_scan_seconds_ago': lastScanSecondsAgo,
+};
+
+/// Shape shared by the mDNS, SSDP and DHCP scanners (passive listeners).
+Map<String, dynamic> listenerScannerJson({
+  bool isListening = false,
+  double? listeningForSeconds,
+  int devicesSeen = 0,
+  double? lastDeviceSeenSecondsAgo,
+}) => {
+  'is_listening': isListening,
+  'listening_for_seconds': listeningForSeconds,
+  'devices_seen': devicesSeen,
+  'last_device_seen_seconds_ago': lastDeviceSeenSecondsAgo,
+};
diff --git a/frontend/test/helpers/pump_app.dart b/frontend/test/helpers/pump_app.dart
new file mode 100644
index 0000000..0678942
--- /dev/null
+++ b/frontend/test/helpers/pump_app.dart
@@ -0,0 +1,60 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/main.dart';
+import 'package:frontend/theme/catppuccin_mocha_theme.dart';
+import 'package:provider/provider.dart';
+
+/// Pumps a single screen/widget under test inside the minimal scaffolding the
+/// app's widgets expect: an [AppState] provider (read by Settings) and a
+/// [MaterialApp] carrying a real app theme. The real theme is required because
+/// several widgets read `Theme.of(context).extension<AppColorExtension>()!`
+/// non-null and would crash under a bare [ThemeData].
+///
+/// Widgets are pumped directly (never through the router shell) so the AppBar's
+/// Google Fonts lookup is never reached.
+Future<void> pumpScreen(
+  WidgetTester tester,
+  Widget child, {
+  Size size = const Size(900, 1200),
+}) async {
+  tester.view.physicalSize = size;
+  tester.view.devicePixelRatio = 1.0;
+  addTearDown(tester.view.resetPhysicalSize);
+  addTearDown(tester.view.resetDevicePixelRatio);
+
+  await tester.pumpWidget(
+    ChangeNotifierProvider(
+      create: (_) => AppState(),
+      child: MaterialApp(
+        theme: catppuccinMochaDarkTheme,
+        home: Scaffold(body: child),
+      ),
+    ),
+  );
+}
+
+/// Pumps frames (advancing fake time in small steps) until [finder] matches or
+/// [maxFrames] is reached. Needed because Dio resolves each request through an
+/// internal zero-duration timer, so the response only lands once the fake clock
+/// is advanced — `pumpAndSettle` is unusable here as the polling widgets keep a
+/// periodic timer alive forever.
+Future<void> pumpUntilFound(
+  WidgetTester tester,
+  Finder finder, {
+  int maxFrames = 40,
+  Duration step = const Duration(milliseconds: 10),
+}) async {
+  for (var i = 0; i < maxFrames; i++) {
+    if (finder.evaluate().isNotEmpty) return;
+    await tester.pump(step);
+  }
+  if (finder.evaluate().isEmpty) {
+    fail('Timed out waiting for $finder');
+  }
+}
+
+/// Unmounts the widget tree so widgets' `dispose()` cancel their timers and the
+/// test ends without "pending timer" failures. Call at the end of widget tests
+/// that exercise polling widgets.
+Future<void> tearDownTree(WidgetTester tester) =>
+    tester.pumpWidget(const SizedBox());
diff --git a/frontend/test/unit/api_error_test.dart b/frontend/test/unit/api_error_test.dart
new file mode 100644
index 0000000..fc75b97
--- /dev/null
+++ b/frontend/test/unit/api_error_test.dart
@@ -0,0 +1,86 @@
+import 'package:dio/dio.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/utils/api/api_error.dart';
+
+void main() {
+  final options = RequestOptions(path: '/x');
+
+  DioException dio(DioExceptionType type, {int? status}) => DioException(
+        requestOptions: options,
+        type: type,
+        response: status == null
+            ? null
+            : Response(requestOptions: options, statusCode: status),
+      );
+
+  test('maps shape errors', () {
+    expect(
+      dioErrorToUserMessage(TypeError()),
+      'Unexpected response shape from backend.',
+    );
+    expect(
+      dioErrorToUserMessage(const FormatException('bad')),
+      'Unexpected response shape from backend.',
+    );
+  });
+
+  test('maps non-Dio errors to a generic message', () {
+    expect(dioErrorToUserMessage(Exception('boom')), 'Unexpected error.');
+  });
+
+  test('maps timeouts', () {
+    expect(
+      dioErrorToUserMessage(dio(DioExceptionType.connectionTimeout)),
+      'Backend did not respond in time.',
+    );
+    expect(
+      dioErrorToUserMessage(dio(DioExceptionType.receiveTimeout)),
+      'Backend did not respond in time.',
+    );
+  });
+
+  test('maps connection and certificate errors', () {
+    expect(
+      dioErrorToUserMessage(dio(DioExceptionType.connectionError)),
+      'Cannot reach backend. Check the base URL and your network.',
+    );
+    expect(
+      dioErrorToUserMessage(dio(DioExceptionType.badCertificate)),
+      'Backend TLS certificate could not be verified.',
+    );
+  });
+
+  test('maps bad responses by status code', () {
+    expect(
+      dioErrorToUserMessage(dio(DioExceptionType.badResponse, status: 401)),
+      'Authentication failed. Check your API key in Settings.',
+    );
+    expect(
+      dioErrorToUserMessage(dio(DioExceptionType.badResponse, status: 403)),
+      'Authentication failed. Check your API key in Settings.',
+    );
+    expect(
+      dioErrorToUserMessage(dio(DioExceptionType.badResponse, status: 404)),
+      'Not found.',
+    );
+    expect(
+      dioErrorToUserMessage(dio(DioExceptionType.badResponse, status: 503)),
+      'Backend error (status 503). Please try again.',
+    );
+    expect(
+      dioErrorToUserMessage(dio(DioExceptionType.badResponse, status: 418)),
+      'Unexpected response from backend (status 418).',
+    );
+  });
+
+  test('maps cancellation and unknown errors', () {
+    expect(
+      dioErrorToUserMessage(dio(DioExceptionType.cancel)),
+      'Request canceled.',
+    );
+    expect(
+      dioErrorToUserMessage(dio(DioExceptionType.unknown)),
+      'Unexpected error contacting backend.',
+    );
+  });
+}
diff --git a/frontend/test/unit/device_event_test.dart b/frontend/test/unit/device_event_test.dart
new file mode 100644
index 0000000..be1f824
--- /dev/null
+++ b/frontend/test/unit/device_event_test.dart
@@ -0,0 +1,43 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/model/device_event.dart';
+
+import '../helpers/fixtures.dart';
+
+void main() {
+  test('DeviceEvent.fromJson maps all fields', () {
+    final event = DeviceEvent.fromJson(
+      deviceEventJson(
+        id: 42,
+        macAddress: '11:22:33:44:55:66',
+        createdOn: '2026-05-20T10:30:00Z',
+        eventType: 'changed',
+        ipv4Address: '10.0.0.9',
+        vendor: 'Initech',
+        scanner: 'Ssdp',
+      ),
+    );
+
+    expect(event.id, 42);
+    expect(event.macAddress, '11:22:33:44:55:66');
+    expect(event.createdOn, DateTime.parse('2026-05-20T10:30:00Z'));
+    expect(event.eventType, 'changed');
+    expect(event.ipv4Address, '10.0.0.9');
+    expect(event.vendor, 'Initech');
+    expect(event.scanner, 'Ssdp');
+  });
+
+  test('scannerLabel humanises known scanner names', () {
+    expect(_label('Arp'), 'ARP');
+    expect(_label('Mdns'), 'mDNS');
+    expect(_label('Ssdp'), 'SSDP/UPnP');
+    expect(_label('Dhcp'), 'DHCP');
+    expect(_label('Snmp'), 'SNMP');
+  });
+
+  test('scannerLabel passes through unknown scanner names', () {
+    expect(_label('Custom'), 'Custom');
+  });
+}
+
+String _label(String scanner) =>
+    DeviceEvent.fromJson(deviceEventJson(scanner: scanner)).scannerLabel;
diff --git a/frontend/test/unit/device_summary_test.dart b/frontend/test/unit/device_summary_test.dart
new file mode 100644
index 0000000..83039e1
--- /dev/null
+++ b/frontend/test/unit/device_summary_test.dart
@@ -0,0 +1,24 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/model/device_summary.dart';
+
+import '../helpers/fixtures.dart';
+
+void main() {
+  test('DeviceSummary.fromJson maps every count field', () {
+    final summary = DeviceSummary.fromJson(
+      deviceSummaryJson(
+        totalRegistered: 10,
+        seenLastDayRegistered: 4,
+        seenLastDayUnregistered: 2,
+        seenLastWeekRegistered: 8,
+        seenLastWeekUnregistered: 5,
+      ),
+    );
+
+    expect(summary.totalRegistered, 10);
+    expect(summary.seenLastDayRegistered, 4);
+    expect(summary.seenLastDayUnregistered, 2);
+    expect(summary.seenLastWeekRegistered, 8);
+    expect(summary.seenLastWeekUnregistered, 5);
+  });
+}
diff --git a/frontend/test/unit/device_test.dart b/frontend/test/unit/device_test.dart
new file mode 100644
index 0000000..7dad422
--- /dev/null
+++ b/frontend/test/unit/device_test.dart
@@ -0,0 +1,43 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/model/device.dart';
+import 'package:frontend/model/device_type.dart';
+
+import '../helpers/fixtures.dart';
+
+void main() {
+  group('Device.fromJson', () {
+    test('maps all snake_case fields', () {
+      final device = Device.fromJson(
+        deviceJson(
+          macAddress: '11:22:33:44:55:66',
+          ipv4Address: '10.0.0.5',
+          vendor: 'Globex',
+          lastSeen: '2026-05-30T08:15:00Z',
+          isRegistered: true,
+          owner: 'bob',
+          deviceType: 'network_appliance',
+          name: 'Router',
+        ),
+      );
+
+      expect(device.macAddress, '11:22:33:44:55:66');
+      expect(device.ipv4Address, '10.0.0.5');
+      expect(device.vendor, 'Globex');
+      expect(device.lastSeen, DateTime.parse('2026-05-30T08:15:00Z'));
+      expect(device.isRegistered, isTrue);
+      expect(device.owner, 'bob');
+      expect(device.deviceType, DeviceType.networkAppliance);
+      expect(device.name, 'Router');
+    });
+
+    test('leaves name null when absent', () {
+      final device = Device.fromJson(deviceJson());
+      expect(device.name, isNull);
+    });
+
+    test('falls back to unknown device type for unrecognised values', () {
+      final device = Device.fromJson(deviceJson(deviceType: 'spaceship'));
+      expect(device.deviceType, DeviceType.unknown);
+    });
+  });
+}
diff --git a/frontend/test/unit/device_type_test.dart b/frontend/test/unit/device_type_test.dart
new file mode 100644
index 0000000..86c4b26
--- /dev/null
+++ b/frontend/test/unit/device_type_test.dart
@@ -0,0 +1,39 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/model/device_type.dart';
+
+void main() {
+  test('fromString parses every snake_case API name', () {
+    expect(DeviceType.fromString('phone'), DeviceType.phone);
+    expect(DeviceType.fromString('network_appliance'), DeviceType.networkAppliance);
+    expect(DeviceType.fromString('home_security'), DeviceType.homeSecurity);
+    expect(DeviceType.fromString('home_appliance'), DeviceType.homeAppliance);
+    expect(DeviceType.fromString('gaming_console'), DeviceType.gamingConsole);
+  });
+
+  test('fromString is case-insensitive', () {
+    expect(DeviceType.fromString('TV'), DeviceType.tv);
+  });
+
+  test('fromString falls back to unknown', () {
+    expect(DeviceType.fromString('toaster'), DeviceType.unknown);
+  });
+
+  test('apiName mirrors the snake_case backend identifiers', () {
+    expect(DeviceType.networkAppliance.apiName, 'network_appliance');
+    expect(DeviceType.gamingConsole.apiName, 'gaming_console');
+    expect(DeviceType.phone.apiName, 'phone');
+  });
+
+  test('apiName round-trips through fromString', () {
+    for (final type in DeviceType.values) {
+      if (type == DeviceType.unknown) continue;
+      expect(DeviceType.fromString(type.apiName), type);
+    }
+  });
+
+  test('label special-cases acronyms', () {
+    expect(DeviceType.tv.label, 'TV');
+    expect(DeviceType.pc.label, 'PC');
+    expect(DeviceType.networkAppliance.label, 'Network Appliance');
+  });
+}
diff --git a/frontend/test/unit/duration_formatter_test.dart b/frontend/test/unit/duration_formatter_test.dart
new file mode 100644
index 0000000..676fa54
--- /dev/null
+++ b/frontend/test/unit/duration_formatter_test.dart
@@ -0,0 +1,27 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/utils/duration_formatter.dart';
+
+void main() {
+  test('renders sub-minute values in seconds', () {
+    expect(formatSeconds(0), '0s');
+    expect(formatSeconds(59), '59s');
+  });
+
+  test('rounds fractional seconds to the nearest whole second', () {
+    expect(formatSeconds(5.4), '5s');
+    expect(formatSeconds(5.6), '6s');
+  });
+
+  test('renders minute-and-second values past 60 seconds', () {
+    expect(formatSeconds(60), '1m 0s');
+    expect(formatSeconds(125), '2m 5s');
+  });
+
+  test('rounding up to a full minute carries into the minutes part', () {
+    expect(formatSeconds(59.6), '1m 0s');
+  });
+
+  test('clamps negative values to zero', () {
+    expect(formatSeconds(-10), '0s');
+  });
+}
diff --git a/frontend/test/unit/friendly_date_formatter_test.dart b/frontend/test/unit/friendly_date_formatter_test.dart
new file mode 100644
index 0000000..b8caa5c
--- /dev/null
+++ b/frontend/test/unit/friendly_date_formatter_test.dart
@@ -0,0 +1,47 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/utils/friendly_date_formatter.dart';
+
+void main() {
+  final formatter = FriendlyDateFormatter();
+  final now = DateTime.now();
+
+  test('renders very recent times as "Just now"', () {
+    expect(formatter.format(now.subtract(const Duration(seconds: 30))), 'Just now');
+    expect(formatter.format(now.subtract(const Duration(minutes: 2))), 'Just now');
+  });
+
+  test('renders times under an hour as relative minutes', () {
+    expect(
+      formatter.format(now.subtract(const Duration(minutes: 30))),
+      '30 minutes ago',
+    );
+  });
+
+  test('renders earlier-today / late-yesterday times with a clock time', () {
+    final candidate = now.subtract(const Duration(hours: 2));
+    final sameDay = candidate.year == now.year &&
+        candidate.month == now.month &&
+        candidate.day == now.day;
+
+    expect(
+      formatter.format(candidate),
+      startsWith(sameDay ? 'Today at' : 'Yesterday at'),
+    );
+  });
+
+  test('renders a yesterday-noon time as "Yesterday at"', () {
+    final yesterdayNoon =
+        DateTime(now.year, now.month, now.day - 1, 12, 0);
+
+    expect(formatter.format(yesterdayNoon), startsWith('Yesterday at'));
+  });
+
+  test('renders older dates with the full date', () {
+    final threeDaysAgo = DateTime(now.year, now.month, now.day - 3, 12, 0);
+    final result = formatter.format(threeDaysAgo);
+
+    expect(result, contains(threeDaysAgo.year.toString()));
+    expect(result, isNot(startsWith('Today')));
+    expect(result, isNot(startsWith('Yesterday')));
+  });
+}
diff --git a/frontend/test/unit/notification_test.dart b/frontend/test/unit/notification_test.dart
new file mode 100644
index 0000000..5912f95
--- /dev/null
+++ b/frontend/test/unit/notification_test.dart
@@ -0,0 +1,61 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/model/notification.dart';
+import 'package:frontend/model/notification_type.dart';
+
+import '../helpers/fixtures.dart';
+
+void main() {
+  group('Notification.fromJson', () {
+    test('maps all fields', () {
+      final notification = Notification.fromJson(
+        notificationJson(
+          id: 9,
+          createdOn: '2026-05-15T09:00:00Z',
+          notificationType: 'deviceChanged',
+          title: 'Device changed',
+          body: 'Something changed',
+          isNew: false,
+          macAddress: '11:22:33:44:55:66',
+        ),
+      );
+
+      expect(notification.id, 9);
+      expect(notification.createdOn, DateTime.parse('2026-05-15T09:00:00Z'));
+      expect(notification.notificationType, NotificationType.deviceChanged);
+      expect(notification.title, 'Device changed');
+      expect(notification.body, 'Something changed');
+      expect(notification.isNew, isFalse);
+      expect(notification.macAddress, '11:22:33:44:55:66');
+    });
+
+    test('leaves macAddress null when absent', () {
+      final notification = Notification.fromJson(
+        notificationJson(macAddress: null),
+      );
+      expect(notification.macAddress, isNull);
+    });
+  });
+
+  test('toJson round-trips back through fromJson', () {
+    final original = Notification.fromJson(notificationJson(id: 3));
+    final restored = Notification.fromJson(original.toJson());
+
+    expect(restored.id, original.id);
+    expect(restored.title, original.title);
+    expect(restored.body, original.body);
+    expect(restored.isNew, original.isNew);
+    expect(restored.notificationType, original.notificationType);
+    expect(restored.createdOn, original.createdOn);
+    expect(restored.macAddress, original.macAddress);
+  });
+
+  test('copyWith only overrides isNew', () {
+    final original = Notification.fromJson(notificationJson(isNew: true));
+    final updated = original.copyWith(isNew: false);
+
+    expect(updated.isNew, isFalse);
+    expect(updated.id, original.id);
+    expect(updated.title, original.title);
+    expect(original.isNew, isTrue, reason: 'original is not mutated');
+  });
+}
diff --git a/frontend/test/unit/notification_type_test.dart b/frontend/test/unit/notification_type_test.dart
new file mode 100644
index 0000000..3092fa5
--- /dev/null
+++ b/frontend/test/unit/notification_type_test.dart
@@ -0,0 +1,30 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/model/notification_type.dart';
+
+void main() {
+  test('fromString parses known types case-insensitively', () {
+    expect(
+      NotificationType.fromString('newDeviceFound'),
+      NotificationType.newDeviceFound,
+    );
+    expect(
+      NotificationType.fromString('deviceonlineaftertime'),
+      NotificationType.deviceOnlineAfterTime,
+    );
+    expect(
+      NotificationType.fromString('DeviceChanged'),
+      NotificationType.deviceChanged,
+    );
+  });
+
+  test('fromString falls back to other', () {
+    expect(NotificationType.fromString('whatever'), NotificationType.other);
+  });
+
+  test('name round-trips through fromString', () {
+    for (final type in NotificationType.values) {
+      if (type == NotificationType.other) continue;
+      expect(NotificationType.fromString(type.name), type);
+    }
+  });
+}
diff --git a/frontend/test/unit/polled_value_test.dart b/frontend/test/unit/polled_value_test.dart
new file mode 100644
index 0000000..1ff29af
--- /dev/null
+++ b/frontend/test/unit/polled_value_test.dart
@@ -0,0 +1,134 @@
+import 'dart:async';
+
+import 'package:dio/dio.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/utils/backend_reachability.dart';
+import 'package:frontend/utils/polled_value.dart';
+
+import '../helpers/backend_test_harness.dart';
+
+void main() {
+  late List<Completer<int>> completers;
+
+  setUp(() async {
+    completers = [];
+    await setUpBackendForTest();
+  });
+
+  // A PolledValue whose every fetch is resolved manually through [completers].
+  // The poll interval is effectively disabled so only explicit reloads fetch.
+  PolledValue<int> makePolled({
+    Duration staleErrorAfter = const Duration(seconds: 30),
+  }) {
+    return PolledValue<int>(
+      fetch: ({cancelToken}) {
+        final completer = Completer<int>();
+        completers.add(completer);
+        return completer.future;
+      },
+      pollInterval: const Duration(hours: 1),
+      staleErrorAfter: staleErrorAfter,
+    );
+  }
+
+  DioException connectionError() => DioException(
+        requestOptions: RequestOptions(path: '/x'),
+        type: DioExceptionType.connectionError,
+      );
+
+  test('starts in initialLoading then becomes fresh on success', () async {
+    final polled = makePolled();
+    addTearDown(polled.dispose);
+
+    expect(polled.freshness, PolledFreshness.initialLoading);
+    expect(polled.value, isNull);
+
+    completers[0].complete(5);
+    await pumpEventQueue();
+
+    expect(polled.freshness, PolledFreshness.fresh);
+    expect(polled.value, 5);
+  });
+
+  test('becomes error when the first load fails with no prior value', () async {
+    final polled = makePolled();
+    addTearDown(polled.dispose);
+
+    completers[0].completeError(connectionError());
+    await pumpEventQueue();
+
+    expect(polled.freshness, PolledFreshness.error);
+    expect(polled.value, isNull);
+    expect(polled.lastErrorMessage, isNotNull);
+  });
+
+  test('a failure after a success is stale, then error past staleErrorAfter',
+      () async {
+    final polled = makePolled(staleErrorAfter: const Duration(seconds: 1));
+    addTearDown(polled.dispose);
+
+    completers[0].complete(1);
+    await pumpEventQueue();
+    expect(polled.freshness, PolledFreshness.fresh);
+
+    // Force a second load and fail it.
+    polled.pause();
+    polled.resume();
+    await pumpEventQueue();
+    completers[1].completeError(connectionError());
+    await pumpEventQueue();
+
+    expect(polled.value, 1, reason: 'keeps the last good value');
+    expect(polled.freshness, PolledFreshness.stale);
+
+    await Future<void>.delayed(const Duration(milliseconds: 1200));
+    expect(polled.freshness, PolledFreshness.error);
+  });
+
+  test('effectiveFreshness downgrades error to stale while offline', () async {
+    final polled = makePolled(staleErrorAfter: const Duration(milliseconds: 1));
+    addTearDown(polled.dispose);
+
+    completers[0].complete(1);
+    await pumpEventQueue();
+    polled.pause();
+    polled.resume();
+    await pumpEventQueue();
+    completers[1].completeError(connectionError());
+    await pumpEventQueue();
+    await Future<void>.delayed(const Duration(milliseconds: 5));
+
+    // Base freshness is error (value present, but past the 1ms threshold).
+    expect(polled.freshness, PolledFreshness.error);
+
+    // Online: effective freshness mirrors the base error.
+    expect(effectiveFreshness(polled), PolledFreshness.error);
+
+    // Offline with a value present: downgraded to stale.
+    BackendReachability.instance.recordFailure(connectionError());
+    expect(BackendReachability.instance.isOnline, isFalse);
+    expect(effectiveFreshness(polled), PolledFreshness.stale);
+  });
+
+  test('pause/resume is reference counted across reasons', () async {
+    final polled = makePolled();
+    addTearDown(polled.dispose);
+
+    completers[0].complete(1);
+    await pumpEventQueue();
+    expect(completers, hasLength(1));
+
+    polled.pauseFor(PolledPauseReason.manual);
+    polled.pauseFor(PolledPauseReason.unreachable);
+
+    // Removing only one of two reasons must not reload.
+    polled.resumeFor(PolledPauseReason.manual);
+    await pumpEventQueue();
+    expect(completers, hasLength(1));
+
+    // Clearing the last reason reloads.
+    polled.resumeFor(PolledPauseReason.unreachable);
+    await pumpEventQueue();
+    expect(completers, hasLength(2));
+  });
+}
diff --git a/frontend/test/unit/scanner_status_models_test.dart b/frontend/test/unit/scanner_status_models_test.dart
new file mode 100644
index 0000000..c53c1dc
--- /dev/null
+++ b/frontend/test/unit/scanner_status_models_test.dart
@@ -0,0 +1,87 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/model/arp_scanner_status.dart';
+import 'package:frontend/model/dhcp_scanner_status.dart';
+import 'package:frontend/model/mdns_scanner_status.dart';
+import 'package:frontend/model/snmp_scanner_status.dart';
+import 'package:frontend/model/ssdp_scanner_status.dart';
+
+import '../helpers/fixtures.dart';
+
+void main() {
+  group('interval scanners (ARP, SNMP)', () {
+    test('ArpScannerStatus.fromJson maps populated fields', () {
+      final status = ArpScannerStatus.fromJson(
+        intervalScannerJson(
+          isRunning: true,
+          runningForSeconds: 12.5,
+          nextRunInSeconds: 30,
+          lastScanDevicesSeen: 7,
+          lastScanSecondsAgo: 5,
+        ),
+      );
+
+      expect(status.isRunning, isTrue);
+      expect(status.runningForSeconds, 12.5);
+      expect(status.nextRunInSeconds, 30.0);
+      expect(status.lastScanDevicesSeen, 7);
+      expect(status.lastScanSecondsAgo, 5.0);
+    });
+
+    test('ArpScannerStatus.fromJson tolerates null optionals', () {
+      final status = ArpScannerStatus.fromJson(intervalScannerJson());
+
+      expect(status.isRunning, isFalse);
+      expect(status.runningForSeconds, isNull);
+      expect(status.nextRunInSeconds, isNull);
+      expect(status.lastScanDevicesSeen, isNull);
+    });
+
+    test('SnmpScannerStatus.fromJson maps fields', () {
+      final status = SnmpScannerStatus.fromJson(
+        intervalScannerJson(isRunning: true, runningForSeconds: 3),
+      );
+
+      expect(status.isRunning, isTrue);
+      expect(status.runningForSeconds, 3.0);
+    });
+  });
+
+  group('listener scanners (mDNS, SSDP, DHCP)', () {
+    test('MdnsScannerStatus.fromJson maps populated fields', () {
+      final status = MdnsScannerStatus.fromJson(
+        listenerScannerJson(
+          isListening: true,
+          listeningForSeconds: 99.0,
+          devicesSeen: 4,
+          lastDeviceSeenSecondsAgo: 8,
+        ),
+      );
+
+      expect(status.isListening, isTrue);
+      expect(status.listeningForSeconds, 99.0);
+      expect(status.devicesSeen, 4);
+      expect(status.lastDeviceSeenSecondsAgo, 8.0);
+    });
+
+    test('SsdpScannerStatus.fromJson requires devicesSeen and tolerates nulls',
+        () {
+      final status = SsdpScannerStatus.fromJson(
+        listenerScannerJson(devicesSeen: 0),
+      );
+
+      expect(status.isListening, isFalse);
+      expect(status.devicesSeen, 0);
+      expect(status.listeningForSeconds, isNull);
+      expect(status.lastDeviceSeenSecondsAgo, isNull);
+    });
+
+    test('DhcpScannerStatus.fromJson maps fields', () {
+      final status = DhcpScannerStatus.fromJson(
+        listenerScannerJson(isListening: true, devicesSeen: 2),
+      );
+
+      expect(status.isListening, isTrue);
+      expect(status.devicesSeen, 2);
+    });
+  });
+}
diff --git a/frontend/test/widget/about_test.dart b/frontend/test/widget/about_test.dart
new file mode 100644
index 0000000..4adb447
--- /dev/null
+++ b/frontend/test/widget/about_test.dart
@@ -0,0 +1,25 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/about/about.dart';
+
+import '../helpers/backend_test_harness.dart';
+import '../helpers/pump_app.dart';
+
+void main() {
+  setUp(() async {
+    await setUpBackendForTest();
+  });
+
+  testWidgets('renders the about content and release fallback', (tester) async {
+    await pumpScreen(tester, const About());
+    // PackageInfo.fromPlatform() has no plugin in tests, so the FutureBuilder
+    // falls back to the hard-coded release date.
+    await tester.pump();
+
+    expect(find.text('About OOTT'), findsOneWidget);
+    // Assert the fallback prefix only, not the release date literal (it changes
+    // every release).
+    expect(find.textContaining('Released'), findsOneWidget);
+    expect(find.text('Source code'), findsOneWidget);
+    expect(find.text('openssl'), findsOneWidget);
+  });
+}
diff --git a/frontend/test/widget/device_list_test.dart b/frontend/test/widget/device_list_test.dart
new file mode 100644
index 0000000..77c6b9d
--- /dev/null
+++ b/frontend/test/widget/device_list_test.dart
@@ -0,0 +1,60 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/devices/device_list.dart';
+import 'package:frontend/devices/device_list_rows.dart';
+import 'package:http_mock_adapter/http_mock_adapter.dart';
+
+import '../helpers/backend_test_harness.dart';
+import '../helpers/fixtures.dart';
+import '../helpers/pump_app.dart';
+
+void main() {
+  late DioAdapter adapter;
+
+  setUp(() async {
+    adapter = await setUpBackendForTest();
+  });
+
+  testWidgets('renders device rows after loading', (tester) async {
+    adapter.onGet(
+      '/devices',
+      (server) => server.reply(200, [
+        deviceJson(macAddress: '00:00:00:00:00:01', owner: 'alice'),
+        deviceJson(macAddress: '00:00:00:00:00:02', owner: 'bob'),
+      ]),
+    );
+
+    await pumpScreen(tester, const DeviceList());
+    await pumpUntilFound(tester, find.byType(DeviceRowWide));
+
+    expect(find.byType(DeviceRowWide), findsNWidgets(2));
+
+    await tearDownTree(tester);
+  });
+
+  testWidgets('shows the empty message when there are no devices',
+      (tester) async {
+    adapter.onGet('/devices', (server) => server.reply(200, <dynamic>[]));
+
+    await pumpScreen(tester, const DeviceList());
+    await pumpUntilFound(tester, find.text('No unregistered devices'));
+
+    expect(find.text('No unregistered devices'), findsOneWidget);
+    expect(find.byType(DeviceRowWide), findsNothing);
+
+    await tearDownTree(tester);
+  });
+
+  testWidgets('shows an error message when the request fails', (tester) async {
+    adapter.onGet('/devices', (server) => server.reply(500, {'error': 'boom'}));
+
+    await pumpScreen(tester, const DeviceList());
+    await pumpUntilFound(
+      tester,
+      find.textContaining('Backend error (status 500)'),
+    );
+
+    expect(find.textContaining('Backend error (status 500)'), findsOneWidget);
+
+    await tearDownTree(tester);
+  });
+}
diff --git a/frontend/test/widget/device_summary_card_test.dart b/frontend/test/widget/device_summary_card_test.dart
new file mode 100644
index 0000000..1ec9a05
--- /dev/null
+++ b/frontend/test/widget/device_summary_card_test.dart
@@ -0,0 +1,70 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/widgets/device_summary_card.dart';
+import 'package:http_mock_adapter/http_mock_adapter.dart';
+
+import '../helpers/backend_test_harness.dart';
+import '../helpers/fixtures.dart';
+import '../helpers/pump_app.dart';
+
+void main() {
+  late DioAdapter adapter;
+
+  setUp(() async {
+    adapter = await setUpBackendForTest();
+  });
+
+  testWidgets('shows a loading spinner before the summary arrives',
+      (tester) async {
+    adapter.onGet(
+      '/devices/summary',
+      (server) => server.reply(200, deviceSummaryJson()),
+    );
+
+    await pumpScreen(tester, const DeviceSummaryCard());
+
+    expect(find.byType(CircularProgressIndicator), findsOneWidget);
+
+    // Let the in-flight request resolve so no Dio timer is left pending.
+    await pumpUntilFound(tester, find.byType(Divider));
+    await tearDownTree(tester);
+  });
+
+  testWidgets('renders the summary numbers after loading', (tester) async {
+    adapter.onGet(
+      '/devices/summary',
+      (server) => server.reply(
+        200,
+        deviceSummaryJson(totalRegistered: 12, seenLastDayRegistered: 3),
+      ),
+    );
+
+    await pumpScreen(tester, const DeviceSummaryCard());
+    await pumpUntilFound(tester, find.text('12'));
+
+    expect(find.text('12'), findsOneWidget);
+    expect(find.text('3'), findsWidgets);
+
+    await tearDownTree(tester);
+  });
+
+  testWidgets('shows the error message when the request fails', (tester) async {
+    adapter.onGet(
+      '/devices/summary',
+      (server) => server.reply(500, {'error': 'boom'}),
+    );
+
+    await pumpScreen(tester, const DeviceSummaryCard());
+    await pumpUntilFound(
+      tester,
+      find.textContaining('Backend error (status 500)'),
+    );
+
+    expect(
+      find.textContaining('Backend error (status 500)'),
+      findsOneWidget,
+    );
+
+    await tearDownTree(tester);
+  });
+}
diff --git a/frontend/test/widget/home_screen_test.dart b/frontend/test/widget/home_screen_test.dart
new file mode 100644
index 0000000..3f54616
--- /dev/null
+++ b/frontend/test/widget/home_screen_test.dart
@@ -0,0 +1,66 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/home/home_screen.dart';
+import 'package:http_mock_adapter/http_mock_adapter.dart';
+
+import '../helpers/backend_test_harness.dart';
+import '../helpers/fixtures.dart';
+import '../helpers/pump_app.dart';
+
+void main() {
+  late DioAdapter adapter;
+
+  setUp(() async {
+    adapter = await setUpBackendForTest();
+  });
+
+  void stubHomeEndpoints() {
+    adapter.onGet(
+      '/notifications',
+      (server) => server.reply(200, [
+        notificationJson(id: 1, title: 'New device found'),
+      ]),
+    );
+    adapter.onGet(
+      '/devices/summary',
+      (server) => server.reply(200, deviceSummaryJson(totalRegistered: 5)),
+    );
+    adapter.onGet(
+      '/arp_scanner/status',
+      (server) => server.reply(200, intervalScannerJson(isRunning: true)),
+    );
+    adapter.onGet(
+      '/mdns_scanner/status',
+      (server) => server.reply(200, listenerScannerJson(isListening: true)),
+    );
+    adapter.onGet(
+      '/ssdp_scanner/status',
+      (server) => server.reply(200, listenerScannerJson()),
+    );
+    adapter.onGet(
+      '/dhcp_scanner/status',
+      (server) => server.reply(200, listenerScannerJson()),
+    );
+    adapter.onGet(
+      '/snmp_scanner/status',
+      (server) => server.reply(200, intervalScannerJson()),
+    );
+  }
+
+  testWidgets('shows notifications, the device summary and scanner statuses',
+      (tester) async {
+    stubHomeEndpoints();
+
+    // Below the 700px breakpoint the home screen uses its single-column layout,
+    // giving the cards full width and avoiding the cramped fixed-width side
+    // column (whose rows overflow under the test font metrics).
+    await pumpScreen(tester, const HomeScreen(), size: const Size(690, 2000));
+    await pumpUntilFound(tester, find.textContaining('New device found'));
+
+    expect(find.textContaining('New device found'), findsOneWidget);
+    expect(find.text('Registered in the system'), findsOneWidget);
+    expect(find.text('5'), findsOneWidget);
+
+    await tearDownTree(tester);
+  });
+}
diff --git a/frontend/test/widget/scanner_status_card_test.dart b/frontend/test/widget/scanner_status_card_test.dart
new file mode 100644
index 0000000..a75a13a
--- /dev/null
+++ b/frontend/test/widget/scanner_status_card_test.dart
@@ -0,0 +1,57 @@
+import 'package:dio/dio.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/widgets/scanner_status_card.dart';
+
+import '../helpers/backend_test_harness.dart';
+import '../helpers/pump_app.dart';
+
+ScannerStatus _resolve(BuildContext context, int value, double elapsed) =>
+    (color: Colors.green, label: 'Value $value', sublabels: ['detail line']);
+
+void main() {
+  setUp(() async {
+    await setUpBackendForTest();
+  });
+
+  testWidgets('shows a spinner, then the resolved label and sublabels',
+      (tester) async {
+    await pumpScreen(
+      tester,
+      ScannerStatusCard<int>(
+        title: 'Probe',
+        fetch: ({cancelToken}) async => 42,
+        resolver: _resolve,
+      ),
+    );
+
+    expect(find.byType(CircularProgressIndicator), findsOneWidget);
+
+    await pumpUntilFound(tester, find.text('Value 42'));
+
+    expect(find.text('Probe'), findsOneWidget);
+    expect(find.text('detail line'), findsOneWidget);
+
+    await tearDownTree(tester);
+  });
+
+  testWidgets('renders an Error state when the fetch fails', (tester) async {
+    await pumpScreen(
+      tester,
+      ScannerStatusCard<int>(
+        title: 'Probe',
+        fetch: ({cancelToken}) async => throw DioException(
+          requestOptions: RequestOptions(path: '/x'),
+          type: DioExceptionType.connectionError,
+        ),
+        resolver: _resolve,
+      ),
+    );
+
+    await pumpUntilFound(tester, find.text('Error'));
+
+    expect(find.text('Error'), findsOneWidget);
+
+    await tearDownTree(tester);
+  });
+}
diff --git a/frontend/test/widget/settings_test.dart b/frontend/test/widget/settings_test.dart
new file mode 100644
index 0000000..b72489f
--- /dev/null
+++ b/frontend/test/widget/settings_test.dart
@@ -0,0 +1,71 @@
+import 'package:encrypter/encrypter/xor.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/settings/settings.dart';
+
+import '../helpers/backend_test_harness.dart';
+import '../helpers/pump_app.dart';
+
+void main() {
+  setUp(() async {
+    await setUpBackendForTest(
+      prefs: {
+        'base_url': 'http://my.server/api',
+        'api_key': XOR().xorEncode('topsecret'),
+        'theme': 'catppuccin_mocha',
+      },
+    );
+  });
+
+  testWidgets('prefills the form from stored preferences', (tester) async {
+    await pumpScreen(tester, const Settings());
+
+    expect(find.text('http://my.server/api'), findsOneWidget);
+    expect(find.text('Catppuccin Mocha'), findsOneWidget);
+  });
+
+  testWidgets('validates an empty base URL when testing the connection',
+      (tester) async {
+    await pumpScreen(tester, const Settings());
+
+    await tester.enterText(find.byType(TextFormField).first, '');
+    await tester.tap(find.widgetWithText(ElevatedButton, 'Test'));
+    await tester.pump();
+
+    expect(find.text('The URL cannot be empty'), findsOneWidget);
+  });
+
+  testWidgets('disables Save once the connection details are edited',
+      (tester) async {
+    await pumpScreen(tester, const Settings());
+    final saveButton = find.widgetWithText(ElevatedButton, 'Save');
+
+    expect(
+      tester.widget<ElevatedButton>(saveButton).onPressed,
+      isNotNull,
+      reason: 'enabled for the unmodified, prefilled form',
+    );
+
+    await tester.enterText(
+      find.byType(TextFormField).first,
+      'http://changed/api',
+    );
+    await tester.pump();
+
+    expect(
+      tester.widget<ElevatedButton>(saveButton).onPressed,
+      isNull,
+      reason: 'disabled until the new connection is tested',
+    );
+  });
+
+  testWidgets('saving the unmodified form shows a success message',
+      (tester) async {
+    await pumpScreen(tester, const Settings());
+
+    await tester.tap(find.widgetWithText(ElevatedButton, 'Save'));
+    await pumpUntilFound(tester, find.text('Settings saved successfully'));
+
+    expect(find.text('Settings saved successfully'), findsOneWidget);
+  });
+}
diff --git a/frontend/test/widget/status_screen_test.dart b/frontend/test/widget/status_screen_test.dart
new file mode 100644
index 0000000..a8850e0
--- /dev/null
+++ b/frontend/test/widget/status_screen_test.dart
@@ -0,0 +1,62 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/status/status_screen.dart';
+import 'package:http_mock_adapter/http_mock_adapter.dart';
+
+import '../helpers/backend_test_harness.dart';
+import '../helpers/fixtures.dart';
+import '../helpers/pump_app.dart';
+
+void main() {
+  late DioAdapter adapter;
+
+  setUp(() async {
+    adapter = await setUpBackendForTest();
+  });
+
+  void stubAllScanners() {
+    adapter.onGet(
+      '/arp_scanner/status',
+      (server) => server.reply(
+        200,
+        intervalScannerJson(isRunning: true, runningForSeconds: 10),
+      ),
+    );
+    adapter.onGet(
+      '/mdns_scanner/status',
+      (server) => server.reply(
+        200,
+        listenerScannerJson(isListening: true, devicesSeen: 2),
+      ),
+    );
+    adapter.onGet(
+      '/ssdp_scanner/status',
+      (server) => server.reply(200, listenerScannerJson()),
+    );
+    adapter.onGet(
+      '/dhcp_scanner/status',
+      (server) => server.reply(200, listenerScannerJson()),
+    );
+    adapter.onGet(
+      '/snmp_scanner/status',
+      (server) => server.reply(200, intervalScannerJson()),
+    );
+  }
+
+  testWidgets('renders each scanner card with its resolved status',
+      (tester) async {
+    stubAllScanners();
+
+    await pumpScreen(tester, const StatusScreen());
+    await pumpUntilFound(tester, find.text('Running'));
+
+    expect(find.text('Status'), findsOneWidget);
+    expect(find.text('ARP Scanner'), findsOneWidget);
+    expect(find.text('mDNS Scanner'), findsOneWidget);
+    expect(find.text('Running'), findsWidgets);
+    expect(find.text('Listening'), findsWidgets);
+    expect(find.byType(CircularProgressIndicator), findsNothing);
+
+    await tearDownTree(tester);
+  });
+}