How do you unit test a MAUI app's logic?

Put testable logic in view models and services (plain .NET classes), then test them with xUnit/NUnit/MSTest in a separate class-library targeting a plain TFM (e.g., net8.0). Because MVVM keeps logic out of the UI, you can instantiate view models, inject fakes, and assert on properties and commands without a device.

[Fact]
public async Task Login_SetsIsBusy_False_After_Complete()
{
    var vm = new LoginViewModel(new FakeAuth());
    await vm.LoginCommand.ExecuteAsync(null);
    Assert.False(vm.IsBusy);
}