@Test
public void testSubtract() {

  assertEquals(
      BigInteger.ZERO,
      new CompUInt128(BigInteger.ZERO).subtract(new CompUInt128(BigInteger.ZERO))
          .toBigInteger()
  );
  assertEquals(
      BigInteger.ONE,
      new CompUInt128(BigInteger.ONE).subtract(new CompUInt128(BigInteger.ZERO))
          .toBigInteger()
  );
  assertEquals(
      BigInteger.ZERO,
      new CompUInt128(BigInteger.ONE).subtract(new CompUInt128(BigInteger.ONE))
          .toBigInteger()
  );
  assertEquals(
      twoTo128.subtract(BigInteger.ONE),
      new CompUInt128(BigInteger.ONE).subtract(new CompUInt128(two))
          .toBigInteger()
  );
}