private static TestSerializationB serializeKey2ToB(TestKey2 key, @Nullable SecretKeyAccess access)
      throws GeneralSecurityException {
    SecretKeyAccess.requireAccess(access);
    return new TestSerializationB(B_2);
  }
Tests for {@link MutableSerializationRegistry}.

<p>We repeat the main tests in SerializationRegistryTest. There really shouldn't be both classes,
but currently this is what we need, and the other is what we should have.
java_src/src/test/java/com/google/crypto/tink/internal/MutableSerializationRegistryTest.java