You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: mod.rs
    path of file: ./repos/joystream/runtime-modules/proposals/discussion/src/tests
    
    the code of the file until where you have to start completion: mod mock;

use frame_support::assert_noop;
use frame_support::dispatch::{DispatchError, DispatchResult};
use frame_system::RawOrigin;
use frame_system::{EventRecord, Phase};
use sp_std::iter::FromIterator;

use crate::*;

pub(crate) use mock::Balances;
pub(crate) use mock::*;

struct Eve
    
fn change_thread_mode_fails_with_exceeded_max_author_list_size() {
    initial_test_ext().execute_with(|| {
        let discussion_fixture = DiscussionFixture::default();

        let thread_id = discussion_fixture
            .create_discussion_and_assert(Ok(1))
            .unwrap();

        let change_thread_mode_fixture = ChangeThreadModeFixture::default_for_thread_id(thread_id)
            .with_mode(ThreadMode::Closed(BTreeSet::from_iter(vec![2, 3, 4, 5, 6])));
        change_thread_mode_fixture
            .call_and_assert(Err(Error::<Test>::MaxWhiteListSizeExceeded.into()));
    });
}