See the test your code fails:

doTest(helper, 'pageIndex', -1, 40);

And your code

	pageIndex(itemIndex) {
	// determines what page an item is on. Zero based indexes
	// this method should return -1 for itemIndex values that are out of range
	}

It always returns undefined because there is no code there. You're working on a different method in your first post.

The error message works like this:

pageIndex(40): expected undefined to equal -1 // <- this was the expected answer 
                            ^
//                  Your code returned this                            

And you can see that when you returned 7 instead.

Thank you)