Leetcode: Merge two sorted lists (Rust)

merge_two_lists.rs

/*
Merge two sorted linked lists and return it as a new sorted list. The new list should be made by splicing together the nodes of the first two lists.

Example:

Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->4


*/

//Definition for singly-linked list. Provided by leetcode, non editable
#[derive(PartialEq, Eq, Clone, Debug)]
pub struct ListNode {
  pub val: i32,
  pub next: Option<Box<ListNode>>
}

impl ListNode {
  #[inline]
  fn new(val: i32) -> Self {
    ListNode {
      next: None,
      val
    }
  }
}

// my solution
pub fn merge_two_lists(l1: Option<Box<ListNode>>, l2: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
  match  (l1, l2) {
    (Some(l), None) => return Some(l),
    (None, Some(r)) => return Some(r),
    (None, None) => return None,
    (Some(l), Some(r)) => {
      if l.val <= r.val {
        return Some(Box::new(ListNode{ next: merge_two_lists(l.next, Some(r)), val: l.val }));
      } else {
        return Some(Box::new(ListNode{ next: merge_two_lists(Some(l), r.next), val: r.val }));
      }
    },
  }
}

#[cfg(test)]
mod test {
  use super::*;

  #[test]
  fn can_merge_1() {
    let input1 = Some(Box::new(ListNode::new(1)));
    let input2 = Some(Box::new(ListNode::new(2)));
    let first_node = ListNode {
      next: Some(Box::new(ListNode::new(2))),
      val: 1
    };

    let expected = Some(Box::new(first_node));
    assert_eq!(expected, merge_two_lists(input1, input2));
  }

  #[test]
  fn can_merge_2() {
    let input1 = None;
    let input2 = Some(Box::new(ListNode::new(2)));

    let expected = Some(Box::new(ListNode::new(2)));
    assert_eq!(expected, merge_two_lists(input1, input2));
  }

  #[test]
  fn can_merge_3() {
    let input1 = Some(Box::new(ListNode::new(2)));
    let input2 = None;

    let expected = input1.clone();
    assert_eq!(expected, merge_two_lists(input1, input2));
  }

  #[test]
  fn can_merge_4() {
    let input1 = None;
    let input2 = None;

    let expected = None;
    assert_eq!(expected, merge_two_lists(input1, input2));
  }
}