pub trait TestKindElement {
type Expr: ExprElement;
// Required methods
fn is_true_test(&self) -> bool;
fn is_false_test(&self) -> bool;
fn is_label_used_test(&self) -> bool;
fn is_label_nused_test(&self) -> bool;
fn is_label_exists_test(&self) -> bool;
fn is_label_nexists_test(&self) -> bool;
fn expr_unchecked(&self) -> &Self::Expr;
fn label_unchecked(&self) -> &str;
}