public void InsertNumberMethod_InvalidValues_ThrowArgumentException()
 {
     Assert.Throws <ArgumentException>(() => NumberFinderNew.NextBiggerThan(-1));
     Assert.Throws <ArgumentException>(() => NumberFinderNew.NextBiggerThan(-900));
 }
 public int?NextBiggerThanTests(int number)
 => NumberFinderNew.NextBiggerThan(number);