Test database setup and teardown in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens if the test database connection is not closed after tests?

Consider an Express app test suite that opens a database connection before tests but does not close it after. What is the likely outcome?

A The database will automatically close the connection after tests finish.

B Tests will run faster because the connection stays open for reuse.

C Tests may hang or timeout because the open connection prevents the process from exiting.

D No effect; tests complete normally and exit immediately.

💡 Hint

Think about what happens when a Node.js process has open resources.

If the database connection remains open, Node.js keeps the event loop active, causing tests to hang or timeout instead of exiting.

📝 Syntax

intermediate

Which code snippet correctly sets up and tears down a test database connection in Express tests?

Choose the code that properly opens a database connection before tests and closes it after all tests run.

A before(() => { db.connect(); }); after(() => { db.disconnect(); });

B beforeAll(async () => { await db.connect(); }); afterAll(async () => { await db.disconnect(); });

C beforeEach(async () => { await db.connect(); }); afterEach(async () => { await db.disconnect(); });

D setup(() => { db.connect(); }); teardown(() => { db.disconnect(); });

💡 Hint

Look for async functions that run once before and after all tests.

beforeAll and afterAll run once before and after all tests, ideal for opening and closing database connections. Using beforeEach/afterEach opens and closes connections for every test, which is inefficient.

🔧 Debug

advanced

Why does this test suite fail with 'Timeout - Async callback was not invoked' error?

Review the test setup code below and identify the cause of the timeout error.

Express

beforeAll(() => {
  db.connect();
});

afterAll(() => {
  db.disconnect();
});

test('sample test', () => {
  expect(true).toBe(true);
});

A The beforeAll and afterAll functions are missing async/await, so the test runner does not wait for connection to finish.

B The test function is missing async keyword, causing the test to timeout.

C The db.connect() and db.disconnect() functions are synchronous and block the event loop.

D The test suite is missing a call to jest.runAllTimers() to complete async operations.

💡 Hint

Consider how asynchronous code should be handled in test lifecycle hooks.

Without async/await or returning a promise, beforeAll and afterAll finish immediately, but the database connection is still pending, causing the test runner to wait indefinitely and timeout.

❓ state_output

advanced

What is the state of the test database after running this setup and teardown code?

Given the following code, what will be the state of the test database after all tests complete?

Express

beforeAll(async () => {
  await db.connect();
  await db.clear();
});

afterAll(async () => {
  await db.disconnect();
});

A The database connection remains open and the database still contains old data.

B The database connection remains open and the database is cleared.

C The database connection is closed but the database still contains old data.

D The database connection is closed and the database is empty (cleared).

💡 Hint

Look at what happens before and after all tests regarding connection and data.

The beforeAll hook connects and clears the database, ensuring it is empty before tests. The afterAll hook disconnects, closing the connection. So after tests, the database is empty and connection closed.

🧠 Conceptual

expert

Why is it important to isolate test database setup and teardown from production database in Express apps?

Explain the main reason for using separate test database setup and teardown processes instead of running tests against the production database.

A To prevent tests from accidentally modifying or deleting real production data, ensuring data safety.

B Because test databases automatically generate fake data, unlike production databases.

C To improve test speed by using a smaller production database copy.

D Because production databases do not support connections from test suites.

💡 Hint

Think about the risks of running tests on live data.

Running tests on production databases risks corrupting or deleting real data. Isolating test databases protects production data and allows safe, repeatable tests.