@Test
    public void shouldRoundTripChange() {
        final Change<byte[]> serialized = serde.serializeParts(null, new Change<>("new", "old"));
        final byte[] legacyFormat = mergeChangeArraysIntoSingleLegacyFormattedArray(serialized);
        final Change<byte[]> decomposedLegacyFormat = FullChangeSerde.decomposeLegacyFormattedArrayIntoChangeArrays(legacyFormat);
        assertThat(
            serde.deserializeParts(null, decomposedLegacyFormat),
            is(new Change<>("new", "old"))
        );
    }
We used to serialize a Change into a single byte[]. Now, we don't anymore, but we still keep this logic here
so that we can produce the legacy format to test that we can still deserialize it.
streams/src/test/java/org/apache/kafka/streams/kstream/internals/FullChangeSerdeTest.java