Testing

Test code that depends on DevicePower and WindowFullscreen without a device, a plugin or a mocking library.

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DevicePower#

Every platform read is a constructor parameter, so a test needs no plugin. idleDuration returns milliseconds.

dart

import 'package:flutter/foundation.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:magic_device/magic_device.dart';

void main() {
  test('a discharging device with an away viewer', () async {
    final DevicePower power = DevicePower(
      batteryState: () async => BatteryState.discharging,
      idleDuration: () async => const Duration(minutes: 5).inMilliseconds,
      platform: TargetPlatform.macOS,
    );

    power.start();
    await power.refreshIdle(); // @visibleForTesting: drive the poll without waiting

    expect(await power.charging, isFalse);
    expect(power.idle, isTrue);

    power.stop();
  });
}

BatteryState comes from package:magic_device/magic_device.dart, so the test does not need battery_plus as a direct dependency.

Lifecycle#

The app lifecycle is the one read that cannot be injected. On every platform but macOS and Windows, drive it through the test binding:

dart

import 'package:flutter/widgets.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:magic_device/magic_device.dart';

void main() {
  final TestWidgetsFlutterBinding binding =
      TestWidgetsFlutterBinding.ensureInitialized();

  test('idle follows the app lifecycle', () {
    final DevicePower power = DevicePower(platform: TargetPlatform.android)
      ..start();

    binding.handleAppLifecycleStateChanged(AppLifecycleState.paused);
    expect(power.idle, isTrue);

    binding.handleAppLifecycleStateChanged(AppLifecycleState.resumed);
    expect(power.idle, isFalse);

    power.stop();
  });
}

WindowFullscreen#

On macOS the first use of WindowFullscreen.instance asks the window for its state over the magic_device/window channel, so any test that reaches it under a macOS override needs a fake window on that channel. Set the override and the fake in setUp, and undo both in tearDown in this order:

dart

import 'package:flutter/foundation.dart';
import 'package:flutter/services.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:magic_device/magic_device.dart';

const MethodChannel channel = MethodChannel('magic_device/window');

void main() {
  TestWidgetsFlutterBinding.ensureInitialized();

  setUp(() {
    debugDefaultTargetPlatformOverride = TargetPlatform.macOS;
    TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger
        .setMockMethodCallHandler(channel, (MethodCall call) async {
      if (call.method == 'isFullScreen') return false;
      return null; // toggleFullScreen
    });
  });

  tearDown(() {
    WindowFullscreen.resetInstance();
    TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger
        .setMockMethodCallHandler(channel, null);
    debugDefaultTargetPlatformOverride = null;
  });

  test('the will-notification moves target ahead of active', () async {
    final WindowFullscreen window = WindowFullscreen.instance;
    await Future<void>.delayed(Duration.zero); // let the first read settle

    // Deliver the notification the plugin would post.
    await TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger
        .handlePlatformMessage(
      channel.name,
      const StandardMethodCodec().encodeMethodCall(
        const MethodCall('willEnterFullScreen'),
      ),
      (ByteData? _) {},
    );

    expect(
      (window.active, window.target, window.transitioning),
      (false, true, true),
    );
  });
}

Reset the instance first, then clear the mock handler, then the override. Resetting the override first leaves the channel handler installed, because the reader only clears its handler while available is true.

That tearDown order is for plain test(). Inside testWidgets the binding checks that every foundation debug variable is unset at the end of the test body, before tearDown runs, so with the override set in setUp end the body with WindowFullscreen.resetInstance(); and debugDefaultTargetPlatformOverride = null;. If you use variant: TargetPlatformVariant.only(TargetPlatform.macOS) instead, leave the override out of setUp (the variant sets it and clears it before tearDown) and still end the body with WindowFullscreen.resetInstance();, so the reader drops its channel handler while the platform is macOS.

The four notifications the plugin posts are willEnterFullScreen, didEnterFullScreen, willExitFullScreen and didExitFullScreen.

DevicePower: the signals the readers replace.
WindowFullscreen: the state the notifications drive.

DevicePower#

Lifecycle#

WindowFullscreen#

Related Documentation#