Determining spiritual gifts can not be broken down to a specific formula or a specialized spiritual test. The Holy Spirit distributes the gifts as He determines (1 Corinthians 12:7-11), and while He may give us a specific gift that we will continually walk in, God calls us to obediently serve Him in all things. He will equip us with whatever gift or gifts we need to accomplish the task He has called us to.
Identifying our spiritual gifts can be accomplished in various ways. Spiritual gift tests, while not to be fully relied upon, can definitely help us understand where our gifting might be. Confirmation from those in authority over us, or others also gives light to our spiritual giftedness. Other people who see us serving the Lord can often identify a spiritual gift in us that we might take for granted or not recognize. Prayer is also important. We can ask God to show us how we are gifted in order to better use our spiritual gifts for His glory.
You can download this free Spiritual Gifts Survey (Lifeway Christian Resources). While this test is not the final authority of what your spiritual gifting are, it is a good place to start that can help you understand where your gifting may begin.