What is the difference between 'it' and 'test' in Jest?

javascript

jest

bdd

testing

byAnton Shumikhin·Aug 21, 2024

In Jest, it and test are aliases that define a test block. test is typically used for straightforward, action-based test descriptions, whereas it lends itself to behavior-oriented BDD style descriptions which read more like a sentence.

test('adds integers correctly', () => {
  // When Math does its job right
  expect(1 + 1).toBe(2);
});

it('should add integers correctly', () => {
  // Trying to trick Math to fail 😈
  expect(1 + 1).toBe(2);
});

Make the choice of it or test based on your team’s terminology preference — their functionality is identical under the hood.

Understanding Aliases

Between it and test, there's more at play than just semantic: it's about turning your tests into informative narratives. it is typically used in behavior-driven development (BDD), where tests document the expected behavior of the unit under test.

// BDD style using `it`
it('processes an API request', () => {
  // Test implementation
});

// Action-based style using `test`
test('processes an API request', () => {
  // Test implementation
});

Decluttering your Test Suites

describe helps group related test cases, improving navigation and structure which becomes invaluable for reporting and maintenance.

describe('A bunch of mathematical operators', () => {
  it('successfully divides numbers', () => {
    // Dividing numbers, hopefully not by zero
  });

  test('performs modulo operation', () => {
    // % is not for comments here
  });
});

Whether to use it or test within describe blocks depends purely on your test description style.

Dodging bullets with Test Exemptions

When you need to skip a test or focus on a specific one, Jest offers variations of it in the form of xit() and fit(). These features are surprisingly handy when you've got a flaky test on the loose!

// Dodging a test bullet for now
xit('promises resolve eventually', () => {
  // I'll be back, promise!
});

// Only this test has your undivided attention
fit('promises sometimes reject', () => {
  // The promise was a lie.
});

Of course, test.skip and test.only exist for test lovers.

Consistent Testing in Large Teams

When working in teams, having a common language is crucial. Therefore, decide as a team whether to use it or test — the decision could be influenced by factors such as existing test frameworks in use or the team's comfort level with the BDD style.

Introduce a linting rule to enforce the chosen style across your codebase. This ensures consistency in test descriptions, improves readability, and makes your code reviewer's life a whole lot easier.

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