Function assert_changes 

pub fn assert_changes<T, F>(before: T, f: F, expected_after: T)
where
    T: PartialEq + Debug,
    F: FnOnce(),

Asserts that a shared value changed to the expected state during closure execution.

This helper is intended for values with shared mutability semantics, such as Rc<Cell<T>>, where the cloned before handle observes the final state.