/** To test if inserting at the first spot works */
  @Test
  public void testInsertFirst() {
    // insert a letter at the first node
    filledTest.insertFirst("X");
    twoTest.insertFirst("Y");
    oneTest.insertFirst("Z");
    emptyTest.insertFirst("A");

    // the first letter should be whatever I've inserted (see above)
    assertEquals("X", filledTest.getFirst());
    assertEquals("Y", twoTest.getFirst());
    assertEquals("Z", oneTest.getFirst());
    assertEquals("A", emptyTest.getFirst());
  }
 /** To create a generic list, and subtly test if insertFirst function works */
 @Before
 public void createList() {
   // create a string called "testString" backwards
   String string = "gnirtStset";
   // go through a for loop
   for (int i = 0; i < string.length(); i++) {
     // create a new node with each letter (starting at the end, which is why I had to make it
     // backwards before)
     filledTest.insertFirst(String.valueOf(string.charAt(i)));
   }
   // create a string called "te" backwards
   String two = "et";
   // go through a for loop
   for (int j = 0; j < two.length(); j++) {
     // create a new node with each letter (starting at the end, which is why I had to make it
     // backwards before)
     twoTest.insertFirst(String.valueOf(two.charAt(j)));
   }
   // create a new node with t
   oneTest.insertFirst("t");
 }