public async Task CanExecute_returns_false_during_execution_and_true_after_completion()
{
var tcs = new TaskCompletionSource <bool>();
var command = new AsyncDelegateCommand <int>(x => tcs.Task);
command.Execute(42);
command.CanExecute(42).Should().BeFalse();
tcs.SetResult(true);
await command.WaitForCompletionAsync();
command.CanExecute(42).Should().BeTrue();
}