@Test
public void sqrt() {

  FieldElement element = MersennePrimeFieldElement.create(2, modulus);
  FieldElement sqrt = element.sqrt();
  BigInteger value = MersennePrimeFieldElement.extractValue(sqrt);
  assertThat(value, Is.is(BigInteger.valueOf(62)));
  element = MersennePrimeFieldElement
      .create("180740608519057052622341767564917758093", bigModulus);
  BigInteger expected = MersennePrimeFieldElement.extractValue(element);
  sqrt = element.sqrt();
  value = MersennePrimeFieldElement.extractValue(sqrt);
  assertThat(value.pow(2).mod(bigModulus.getPrime()), Is.is(expected));
}