下面是代码的图片，也在页面底部的超链接“junit”中。我目前有两个测试，编码为“method:insert”，您可以在左侧看到。我需要的主要代码去绿色，也得到100%的覆盖面，我目前在78%。我需要添加什么才能通过junit？朱尼特

This is my JUNIT test code: 
 @Test
 public void testInsert() {
     SortedIntegerList list = new SortedIntegerList();
     list.insert(1);
     list.insert(2);
     Integer output = list.getLast();
     assertNotNull(output);
     SortedIntegerList list2 = new SortedIntegerList();
     list2.insert(1);
     list2.insert(2);
     Integer data = 0;
     assertNotNull(data);
 }
 @Test 
 public void testInsertif() { 
     SortedIntegerList list = new SortedIntegerList();
     list.insert(1);
     Integer result = list.getLast();
     assertNotNull(result);
 }

 @Test 
 public void testInsertwhile() { 
     SortedIntegerList list = new SortedIntegerList();
     list.insert(1);
 }

This is the insert Code: 
 public void insert(Integer data) {
        Node curr, foll;

        if ((first == null) || (data <= first.data)) {
            first = new Node(data, first);
        } else {
            curr = first;
            foll = first.next;
            while ((foll != null) && (foll.data < data)) {
                curr = foll;
                foll = foll.next;
            }
            curr.next = new Node(data, foll);
        }
    }