How do I junit test for the boolean insert(int index, object update) method pls..

You should first define the exact behaviour you are expecting from your insert function. As far as we can see, it does not insert anything to anything.

You are just creating an index variable that goes from 0 to (length - 1).
Then you test for index if it is between 0 and length (inclusive).
index will never be less than zero (because its first initialization value is zero).
index will never be greater than length (the loop will exit before that happens).

So, you have to clearly define and understand the behaviour that you need; then write down on a paper the different steps that you will need. And finally, use what you wrote down to code your function and test it.