public void Nested_Index()
        {
            // $ ./app-nested
            var commandProvider       = new CoconaCommandProvider(new[] { typeof(TestCommands_Nested) });
            var commandCollectionRoot = commandProvider.GetCommandCollection();
            var commandStack          = Array.Empty <CommandDescriptor>();

            var targetCommand     = BuiltInPrimaryCommand.GetCommand(string.Empty); // `TestCommands_Multiple` has no primary command. Use BuiltInPrimaryCommand.
            var commandCollection = commandCollectionRoot;

            var appContext = new CoconaAppContext(targetCommand, default);

            appContext.Features.Set <ICoconaCommandFeature>(new CoconaCommandFeature(commandCollection, targetCommand, commandStack, new object() /* unused */));
            var helpBuilder = new CoconaHelpMessageBuilder(
                new FakeAppContextAccessor(appContext),
                new FakeCommandHelpProvider(),
                new FakeHelpRenderer(),
                commandProvider
                );

            var help = helpBuilder.BuildAndRenderForCurrentContext();

            help.Should().Be("IndexHelp;Commands=Foo,Bar,TestCommands_Nested_1;SubCommandStack=");
        }