def t03_SharingIsPassByReference(C, pks, crypto, server):
    """Verifies that updates to a file are sent to all other users who have that
    file."""
    alice = C("alice")
    bob = C("bob")
    alice.upload("k", "v")
    m = alice.share("bob", "k")
    bob.receive_share("alice", "k", m)
    score = bob.download("k") == "v"
    bob.upload("k", "q")
    score += alice.download("k") == "q"
    return score / 2.0