consistent-each-for.md

vitest/consistent-each-for

📝 Enforce using .each or .for consistently.

⚠️ This rule warns in the 🌐 all config.

Rule Details

Vitest provides two ways to run parameterized tests: .each and .for. This rule enforces consistency in the usage of these methods.

Key Differences:

• .each: Spreads array arguments to individual parameters
• .for: Keeps arrays intact, provides better TestContext support

This rule allows you to configure which method to prefer for different test function types (test, it, describe, suite).

Examples of incorrect code when configured to prefer .for:

// { test: 'for' }
test.each([[1, 1, 2]])('test', (a, b, expected) => {
  expect(a + b).toBe(expected)
})

// { describe: 'for' }
describe.each([[1], [2]])('suite %s', (n) => {
  test('test', () => {})
})

Examples of correct code when configured to prefer .for:

// { test: 'for' }
test.for([[1, 1, 2]])('test', ([a, b, expected]) => {
  expect(a + b).toBe(expected)
})

// { describe: 'for' }
describe.for([[1], [2]])('suite %s', ([n]) => {
  test('test', () => {})
})

Examples of incorrect code when configured to prefer .each:

// { test: 'each' }
test.for([[1, 1, 2]])('test', ([a, b, expected]) => {
  expect(a + b).toBe(expected)
})

Examples of correct code when configured to prefer .each:

// { test: 'each' }
test.each([[1, 1, 2]])('test', (a, b, expected) => {
  expect(a + b).toBe(expected)
})

// { test: 'each' }
test.skip.each([[1, 2]])('test', (a, b) => {
  expect(a).toBeLessThan(b)
})

Options

Name	Description	Type	Choices
describe	Preferred method for describe.	String	each, for
it	Preferred method for it.	String	each, for
suite	Preferred method for suite.	String	each, for
test	Preferred method for test.	String	each, for

Configuration

Typical configuration to enforce .for for tests and .each for describe blocks:

// eslint.config.js
export default [
  {
    rules: {
      'vitest/consistent-each-for': [
        'warn',
        {
          test: 'for',
          it: 'for',
          describe: 'each',
          suite: 'each',
        },
      ],
    },
  },
]

You can configure each function type independently. If a function type is not configured, the rule won't enforce any preference for it.