valid-expect.md

vitest/valid-expect

📝 Enforce valid expect() usage.

💼⚠️ This rule is enabled in the ✅ recommended config. This rule warns in the 🌐 all config.

🔧 This rule is automatically fixable by the --fix CLI option.

This rule triggers a warning if expect is called with no argument or with more than one argument. You change that behavior by setting the minArgs and maxArgs options.

Options

Name	Description	Type
alwaysAwait	Require awaiting every async assertion.	Boolean
asyncMatchers	Matchers that should be considered async assertions.	String[]
maxArgs	Maximum number of arguments allowed for expect.	Number
minArgs	Minimum number of arguments allowed for expect.	Number

1. alwaysAwait

• Type: boolean

• Default: false

• Enforce expect to be called with an await expression.

  // ✅ good
  await expect(Promise.resolve(1)).resolves.toBe(1)
  await expect(Promise.reject(1)).rejects.toBe(1)
  
  // ❌ bad
  expect(Promise.resolve(1)).resolves.toBe(1)
  expect(Promise.reject(1)).rejects.toBe(1)

2. asyncMatchers

• Type: string[]
• Default: []

{
	"vitest/valid-expect": ["error", {
	  "asyncMatchers": ["toBeResolved", "toBeRejected"]
	}]
}

avoid using asyncMatchers with expect:

3. minArgs

• Type: number

• Default: 1

• Enforce expect to be called with at least minArgs arguments.

  // ✅ good
  expect(1).toBe(1)
  expect(1, 2).toBe(1)
  expect(1, 2, 3).toBe(1)
  
  // ❌ bad
  expect().toBe(1)
  expect(1).toBe()

4. maxArgs

• Type: number

• Default: 1

• Enforce expect to be called with at most maxArgs arguments.

• Exception: expect(value, "message") is allowed.

  // ✅ good
  expect(1).toBe(1)
  expect(1, 'expect value to be one').toBe(1)
  const message = 'expect value to be one'
  expect(1, `Error Message: ${message}`).toBe(1)
  
  // ❌ bad
  expect(1, 2, 3, 4).toBe(1)