fn a_config_set_form() -> Modal {

    Modal::Form(Form::config_set(

        crate::widgets::Editor::new(EditMode::Emacs),

        crate::widgets::Editor::new(EditMode::Emacs),

    ))

}

fn empty_stack_has_no_top() {

    let stack = OverlayStack::new();

    assert!(stack.is_empty());

    assert!(stack.top().is_none());

}

fn push_then_pop_yields_last_in_first_out() {

    let mut stack = OverlayStack::new();

    stack.push(Modal::Help);

    stack.push(a_config_set_form());

    let popped = stack.pop().expect("expected a modal");

    assert!(matches!(popped, Modal::Form(_)));

    assert!(matches!(stack.top(), Some(Modal::Help)));

    assert!(!stack.is_empty());

}

fn pop_on_empty_returns_none() {

    let mut stack = OverlayStack::new();

    assert!(stack.pop().is_none());

}

fn top_mut_allows_mutating_focus_field() {

    let mut stack = OverlayStack::new();

    stack.push(a_config_set_form());

    if let Some(Modal::Form(f)) = stack.top_mut() {

        f.focus = 1;

    }

    match stack.top() {

        Some(Modal::Form(f)) => assert_eq!(f.focus, 1),

}