def METHOD_NAME():
    c = FirstChunkCache(5, letters_fetcher, 52)
    assert c.cache is None
    assert c._fetch(12, 15) == letters_fetcher(12, 15)
    assert c.cache is None
    assert c._fetch(3, 10) == letters_fetcher(3, 10)
    assert c.cache == letters_fetcher(0, 5)
    c.fetcher = None
    assert c._fetch(1, 4) == letters_fetcher(1, 4)