In West Virginia and many other states, agreeing to perform field sobriety tests is completely voluntary. However, officers are trained to try convincing you to submit to the tests even though they will rarely tell you that it's your choice.
Why do the police want you to do the tests? Simple. They are after evidence to use against you. The reality is that the tests have very low reliability, they have nothing to do with driving ability (according to the lead researcher who developed the tests), and they are likely to be failed by just about everyone because the outcome is based strictly on the officer's subjective interpretation of how well you did or didn't do.
Because the tests are voluntary, you do not have to submit to them no matter what the officer might say. Likewise, in West Virginia, you do not have to agree to provide a breath sample on the handheld breath gadget. Voluntary means just that - these tests are all voluntary. So, when you know you don't have to submit to these tests and you know they are biased against you, why would you take them?
Be assured that most officers will try to intimidate you into agreeing to their tests and that you will most likely be arrested anyway. However, performing the tests is rarely ever going to lead to you being released. Since you are likely to be arrested in the end no matter what, don't submit to things that the law says you don't have to do, regardless of how hard the officer may be on you.
Just be patient, don't back down from your right to decline the tests, and hire an experienced DUI lawyer to help defend you against the charge.