Background

What I was trying

I was trying to building unit test with Jest for deleting categories.

What I was doing

With using mongodb-memory-server package, I tried to

Initialize fake database for unit testing,
Delete all collections created during testing and,
Disconnect fake database.

For this, I used beforeAll() for initializing fake database and afterAll() for post-testing operations.

deleteCategory.test.ts

import {
  connectFakeDB,
  disconnectFakeDB,
  deleteCollections,
} from "../../utils/fakeDB";
import Category from "../../../src/models/categoryModel";

beforeAll(async () => {
  connectFakeDB();

  const category = new Category({
    category: "existing_example_category",
  });
  await category.save();
});

afterAll(async () => {
  deleteCollections();
  disconnectFakeDB();
});

Problem

But then I got an error in terminal console as below.

● Test suite failed to run

    MongoTopologyClosedError: Topology is closed

      24 |       await collection.deleteMany({});
      25 |     }
    > 26 |   }
         |    ^
      27 | };
      28 |

      at processWaitQueue (node_modules/.pnpm/mongodb@6.7.0/node_modules/mongodb/src/sdam/topology.ts:918:42)
      at Topology.selectServer (node_modules/.pnpm/mongodb@6.7.0/node_modules/mongodb/src/sdam/topology.ts:601:5)
      at retryOperation (node_modules/.pnpm/mongodb@6.7.0/node_modules/mongodb/src/operations/execute_operation.ts:266:33)
      at executeOperation (node_modules/.pnpm/mongodb@6.7.0/node_modules/mongodb/src/operations/execute_operation.ts:199:20)
      at ListCollectionsCursor._initialize (node_modules/.pnpm/mongodb@6.7.0/node_modules/mongodb/src/cursor/list_collections_cursor.ts:44:22)
      at ListCollectionsCursor.[kInit] (node_modules/.pnpm/mongodb@6.7.0/node_modules/mongodb/src/cursor/abstract_cursor.ts:657:21)
      at next (node_modules/.pnpm/mongodb@6.7.0/node_modules/mongodb/src/cursor/abstract_cursor.ts:763:7)
      at ListCollectionsCursor.next (node_modules/.pnpm/mongodb@6.7.0/node_modules/mongodb/src/cursor/abstract_cursor.ts:401:12)
      at ListCollectionsCursor.[Symbol.asyncIterator] (node_modules/.pnpm/mongodb@6.7.0/node_modules/mongodb/src/cursor/abstract_cursor.ts:312:26)
      at ListCollectionsCursor.toArray (node_modules/.pnpm/mongodb@6.7.0/node_modules/mongodb/src/cursor/abstract_cursor.ts:449:22)
      at CollectionsOperation.execute (node_modules/.pnpm/mongodb@6.7.0/node_modules/mongodb/src/operations/collections.ts:31:23)
      at executeOperation (node_modules/.pnpm/mongodb@6.7.0/node_modules/mongodb/src/operations/execute_operation.ts:168:14)
      at Db.collections (node_modules/.pnpm/mongodb@6.7.0/node_modules/mongodb/src/db.ts:418:12)
      at deleteCollections (__tests__/utils/fakeDB.ts:26:29)

Analysis

Looking carefully in the code, there seemed to be a problem in code of deleting collections.

Referring to the response of CameronBurkohlder's response, I just found out that I did not make deleteCollections() method be awaited before disconnecting fake database.

Solution

I solved problem simply putting await syntax keyword in both deleteCollections() and disconnectFakeDB() methods.