message: test(interface-types) Improve test cases for `Stack`.
diff: @@ -100,7 +100,9 @@ mod tests {
  assert_eq!(stack.pop(1), Some(vec![6]));
  assert_eq!(stack.pop(2), Some(vec![5, 4]));
  + assert_eq!(stack.pop(4), None); // not enough items
  assert_eq!(stack.pop(3), Some(vec![3, 2, 1]));
  + assert_eq!(stack.pop1(), None);
  assert_eq!(stack.is_empty(), true);
  }
  }
  