in src/ui.rs [65:74]
fn user_input(&self) -> Result<String> {
let mut inner = self.inner.borrow_mut();
if inner.pending.is_empty() {
panic!("mock is not ready for user input");
}
let remaining = inner.pending.split_off(1);
let first = inner.pending.pop().unwrap();
inner.pending = remaining;
return Ok(first);
}