public Entry getPostingList(long key) {
        return dictionary.get(key);
    }
@Test
    void requireThatEntriesAreSortedOnId() {
        SimpleIndex.Builder builder = new SimpleIndex.Builder();
        builder.insert(KEY, new Posting(DOC_ID, 10));
        builder.insert(KEY, new Posting(DOC_ID - 1, 20));  // Out of order
        builder.insert(KEY, new Posting(DOC_ID + 1, 30));
        SimpleIndex index = builder.build();
        SimpleIndex.Entry entry = index.getPostingList(KEY);
        assertEquals(3, entry.docIds.length);
        assertEquals(DOC_ID - 1, entry.docIds[0]);
        assertEquals(DOC_ID, entry.docIds[1]);
        assertEquals(DOC_ID + 1, entry.docIds[2]);
    }