@Test
  public void testContractExpand() {
    for (int i = 0; i < NUM_BASIC_TESTS; i++) {
      byte[] xBytes = toLittleEndian(x[i]);
      byte[] result = Field25519.contract(Field25519.expand(xBytes));
      assertArrayEquals(xBytes, result);
    }
  }
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