BetRepositoryContract.ts

// inject a function that provides the interface under contract testing
function betRepositoryContract(getRepository: () => BetRepository) {

    test('register a bets', async () => {
        expect(true).toEqual(false);
    })

    test('bets outside range are not retrieved', async () => {
        expect(true).toEqual(false);
    })
}

MongoDbBetRepository.spec.ts

// Do the initialisation ant then call the contract function
describe('MongoDbBetRepository', () => {
    let mongoClient: MongoClient;
    let repository: MongoDbBetRepository;

    beforeEach(async () => {
        mongoClient = new MongoClient('mongodb://localhost:27017');
        const db = await initDb();
        repository = new MongoDbBetRepository(db);
    })

    betRepositoryContract(() => repository);

    afterEach(() => {
        mongoClient.close()
    })

    async function initDb() {
        await mongoClient.connect()
        const db = mongoClient.db('contract_testing');
        await db.collection("bets").drop();
        return db;
    }

})