private static TestSerializationA serializeKey2ToA(TestKey2 key, @Nullable SecretKeyAccess access)
      throws GeneralSecurityException {
    SecretKeyAccess.requireAccess(access);
    return new TestSerializationA(A_2);
  }
Thread safety tests for {@link MutableSerializationRegistry}.
java_src/src/test/java/com/google/crypto/tink/internal/MutableSerializationRegistryMultithreadTest.java