long q = BigInteger.probablePrime(bits, rand).longValue();
        assertFalse(LongMath.isPrime(p * q));
      }
    }
  }

  @GwtIncompatible // isPrime is GWT-incompatible
  public void testIsPrimeThrowsOnNegative() {
    assertThrows(IllegalArgumentException.class, () -> LongMath.isPrime(-1));
  }

  private static final long[] roundToDoubleTestCandidates = {
    0,
    16,
    1L << 53,