public void ShouldPrintNextNumberInput3()
 {
     NaturalNumbers nats = new NaturalNumbers();
     int input = 3;
     int expected = 4;
     int actual = nats.GetNext(input);
     Assert.AreEqual(expected, actual);
 }
 public void ShouldPrintNextNumber()
 {
     NaturalNumbers nats = new NaturalNumbers();
     BigInteger input = nats.GetFirst();
     BigInteger expected = 2;
     BigInteger actual = nats.GetNext(input);
     Assert.AreEqual(expected, actual);
 }