public void NegateString()
 {
     Assert.Throws <ArgumentException>(() => NumberUtils.Negate(string.Empty));
 }
 public void Negate()
 {
     Assert.AreEqual(-10, NumberUtils.Negate(10));
 }
 public void NegateNull()
 {
     Assert.Throws <ArgumentException>(() => NumberUtils.Negate(null));
 }