Test lifecycle hooks (before, after) in Node.js - Step-by-Step Execution

Concept Flow - Test lifecycle hooks (before, after)

Start Test Suite

↓

Run before hook

↓

Run each test

↓

Run after hook

↓

End Test Suite

The test suite starts by running the 'before' hook once, then runs all tests, and finally runs the 'after' hook once.

Execution Sample

Node.js

const assert = require('assert');
before(() => { console.log('Setup'); });
after(() => { console.log('Cleanup'); });
describe('Sample', () => {
  it('test 1', () => { assert.strictEqual(1, 1); });
  it('test 2', () => { assert.strictEqual(2, 2); });
});

This code runs a setup before tests, two tests, then a cleanup after all tests.

Execution Table

Step	Action	Output	Notes
1	Run before hook	Setup	Runs once before all tests
2	Run test 1	Pass	First test runs
3	Run test 2	Pass	Second test runs
4	Run after hook	Cleanup	Runs once after all tests
5	End	All tests done	Test suite finished

💡 All tests executed; before and after hooks run once each.

Variable Tracker

Variable	Start	After before hook	After test 1	After test 2	After after hook
setupDone	false	true	true	true	true
testsRun	0	0	1	2	2
cleanupDone	false	false	false	false	true

Key Moments - 2 Insights

Why does the 'before' hook run only once before all tests?

The 'before' hook is designed to prepare the environment once before any tests run, as shown in execution_table step 1.

Does the 'after' hook run after each test or once after all tests?

The 'after' hook runs once after all tests complete, not after each test, as seen in execution_table step 4.

Visual Quiz - 3 Questions

Look at the execution table, what is the output at step 2?

A Setup

B Pass

C Cleanup

D Fail

💡 Hint

Check the 'Output' column for step 2 in the execution_table.

At which step does the cleanup happen according to the execution table?

A Step 1

B Step 2

C Step 4

D Step 5

💡 Hint

Look for 'Cleanup' in the 'Output' column.

If we add a third test, how would 'testsRun' change after that test in variable_tracker?

A It would become 3

B It would stay 2

C It would reset to 0

D It would become 4

💡 Hint

See how 'testsRun' increments after each test in variable_tracker.

Concept Snapshot

Test lifecycle hooks run code at specific times:
- before(): runs once before all tests
- after(): runs once after all tests
- Tests run between these hooks
Use them to setup and cleanup test environment.

Full Transcript

In Node.js testing, lifecycle hooks like before and after help run code before and after tests. The before hook runs once before any tests start, setting up the environment. Then each test runs one by one. After all tests finish, the after hook runs once to clean up. This flow ensures tests run in a prepared environment and resources are cleaned after. The execution table shows the order: before hook runs first, then tests, then after hook. Variables track setup and cleanup states. This helps beginners see when and how hooks run in relation to tests.