vitest-dev/vitest · error · Error

Expected is not a Number

Error message

Expected is not a Number

What it means

Thrown by the CloseTo asymmetric matcher constructor when the sample is not a number (isA('Number') fails). closeTo asserts the received number is within a tolerance of the sample, so the expected value must be numeric.

Source

Thrown at packages/expect/src/jest-asymmetric-matchers.ts:346

    return this.inverse ? !result : result
  }

  toString() {
    return `String${this.inverse ? 'Not' : ''}Matching`
  }

  getExpectedType() {
    return 'string'
  }
}

class CloseTo extends AsymmetricMatcher<number> {
  private readonly precision: number

  constructor(sample: number, precision = 2, inverse = false) {
    if (!isA('Number', sample)) {
      throw new Error('Expected is not a Number')
    }

    if (!isA('Number', precision)) {
      throw new Error('Precision is not a Number')
    }

    super(sample)
    this.inverse = inverse
    this.precision = precision
  }

  asymmetricMatch(other: number) {
    if (!isA('Number', other)) {
      return false
    }

    let result = false
    if (

View on GitHub (pinned to d568f8ce37)

Solutions

1. Pass a numeric sample: expect.closeTo(3.14159, 4).
2. Coerce with Number() only if you are certain it is numeric.
3. Use a different matcher for non-numeric closeness.

Example fix

// before
expect(result).toEqual(expect.closeTo('3.14', 2))
// after
expect(result).toEqual(expect.closeTo(3.14, 2))

function asNumber(v: unknown): number {
  if (typeof v !== 'number' || Number.isNaN(v)) {
    throw new TypeError(`closeTo needs a number, got ${typeof v}`)
  }
  return v
}
expect(result).toEqual(expect.closeTo(asNumber(sample), precision))

function isFiniteNumber(v: unknown): v is number {
  return typeof v === 'number' && !Number.isNaN(v)
}

When it happens

Trigger: Constructing expect.closeTo(value) (or .not.closeTo) where value is a string, object, null, etc. The first guard in the constructor throws.

Common situations: Passing a string that looks numeric ('3.14'); passing undefined; a variable typed loosely that holds a non-number after a refactor.

Related errors

• Expected is not a string
• You must provide an object to ${this.toString()}, not '${typ
• You must provide an array to ${this.toString()}, not '${type
• any() expects to be passed a constructor function. Please pa
• Expected is not a String or a RegExp

AI-assisted analysis of vitest-dev/vitest@d568f8ce37 (2026-08-03). Data as JSON: /data/errors/f944ce2f2e759671.json. Report an issue: GitHub.