[bug] in Unit test

UserTest.java relies on student properly deleting users and their related data

@After
  public void tearDownClass() {
    MongoDatabase db = mongoClient.getDatabase(databaseName);
    db.getCollection("users").deleteMany(new Document("email", email));
    db.getCollection("users").deleteMany(new Document("email", "log@out.com"));
    db.getCollection("sessions").deleteMany(new Document("user_id", "log@out" +
            ".com"));
  }

you should add

db.getCollection("sessions").deleteMany(new Document("user_id",email));

also consider removing the last statement in the setup method

mongoClient
        .getDatabase(databaseName)
        .getCollection("users")
        .deleteOne(new Document("email", "log@out.com"));