FakeOsIntentsPlatform class

The platform, replaced by something a test can look inside.

Without one, everything OsIntents offers beyond running a handler is invisible in tests: the default implementation of the platform interface answers false and an empty list to keep a plugin-less desktop build working, so a test of code that donates, publishes static answers or pushes a launcher shortcut passes whether or not that code did anything at all.

late FakeOsIntentsPlatform platform;

setUp(() async {
  platform = FakeOsIntentsPlatform.install();
  await OsIntents.install($osIntentsRegistry);
});

test('completing a task donates it', () async {
  await completeTask('t-1');
  expect(platform.donations.single.id, 'completeTask');
});

It is also the only way to exercise the path the OS actually takes. IntentHarness calls a handler directly; invokeIntent goes through the dispatcher OsIntents.install registered, so what it returns is the wire map the system would have been handed — including how a thrown exception is turned into an error the user can be shown.