You test full product life cycle, from purchase to sale with stock qty = 0 at start. Also check the values on the quants list - menu Warehouse/Quants.

At the first I have make inventory adjustment with the quantities I have, and then I have created some purchase orders, delivery orders and so on. But it showing that the inventory value for that item is zero. I have checked the item configuration, I have set the inventory valuation for the item to be real time and also the costing method to be real price. If I chaged the costing method to be average price, or standard price, the inventory value will come but it will not be FIFO. it will take the cost price as a fixed price. but If I changed it again to be real price it will come zero in the inventory valuation.