use std::time::{Duration, SystemTime};

// Adding the smallest possible Duration to SystemTime::MAX shall fail ...
assert!(SystemTime::MAX.checked_add(Duration::new(0, 1)).is_none());

// ... whereas subtracting it shall be fine.
assert!(SystemTime::MAX.checked_sub(Duration::new(0, 1)).is_some());

// Subtracting the smallest possible Duration from SystemTime::MIN shall fail ...
assert!(SystemTime::MIN.checked_sub(Duration::new(0, 1)).is_none());

// ... whereas adding it shall be fine.
assert!(SystemTime::MIN.checked_add(Duration::new(0, 1)).is_some());