deride/jest — jest matchers

Same matcher set as deride/vitest, registered via jest's expect.extend. Import once (ideally from setupFilesAfterEach) and the matchers become available on every test.

Install & register

deride declares jest as an optional peer dependency. If you're using jest you already have it installed (plus @jest/globals for ESM projects).

// jest.setup.ts
import 'deride/jest'

// jest.config.js
module.exports = {
  setupFilesAfterEach: ['./jest.setup.ts'],
}

Available matchers

Matcher	Meaning
toHaveBeenCalled()	At least one call recorded
toHaveBeenCalledTimes(n)	Exactly n calls
toHaveBeenCalledOnce()	Exactly 1 call
toHaveBeenCalledWith(...args)	Any call's args match (matcher-aware, partial)
toHaveBeenLastCalledWith(...args)	The last call's args match
toHaveBeenNthCalledWith(n, ...args)	The 1-indexed n-th call's args match

All support .not:

expect(mock.spy.greet).not.toHaveBeenCalledWith('wrong')

Usage

The API is identical to the vitest integration:

import 'deride/jest'
import { stub, match } from 'deride'

describe('Svc', () => {
  it('records calls', () => {
    const mock = stub<Svc>(['greet'])
    mock.greet('alice')

    expect(mock.spy.greet).toHaveBeenCalledOnce()
    expect(mock.spy.greet).toHaveBeenCalledWith('alice')
    expect(mock.spy.greet).toHaveBeenCalledWith(match.string)
  })
})

For MockedFunctions (from func() or wrap(fn)), pass the function directly — no .spy indirection needed:

const fn = func<(x: number) => number>()
fn(5)
expect(fn).toHaveBeenCalledOnce()
expect(fn).toHaveBeenCalledWith(5)

Coexistence with jest's built-in matchers

jest's toHaveBeenCalled* family works on jest.fn() via .mock.calls. deride's family works on mock.spy.* / MockedFunction via CallRecord[]. Both can be used in the same test — jest delegates to whichever matcher's received shape is satisfied.

Guarded install

The sub-path checks for expect.extend before registering, so importing it in an environment where jest isn't in scope (e.g. if you accidentally load it in a build) is harmless — it becomes a no-op instead of throwing.

ESM note

In jest ESM projects, you may need @jest/globals for expect to be in scope. deride's jest.ts doesn't import jest itself — it looks for a global expect at runtime. If expect isn't globally available (which can happen in some ESM configs), import it explicitly in your setup file:

import { expect } from '@jest/globals'
import 'deride/jest'

Troubleshooting

• Matcher not found — make sure the import ran. Put it in setupFilesAfterEach (not setupFiles, which runs before expect is wired up).
• "expected a MethodSpy or MockedFunction" — pass mock.spy.method, not mock.expect.method.

See the vitest integration for the same matcher set with slightly different error-message formatting. The underlying implementation is shared — src/matchers-runtime.ts.