@Before
  public void setUp() {
    for (int i = 0; i < NUM_BASIC_TESTS; i++) {
      x[i] = (new BigInteger(FIELD_LEN * 8, rand)).mod(P);
      y[i] = (new BigInteger(FIELD_LEN * 8, rand)).mod(P);
    }
  }
The idea of basic tests is simple. We generate random numbers, make computations with
Field25519 and compare the results with Java BigInteger.
java_src/src/test/java/com/google/crypto/tink/internal/Field25519Test.java