Jest mock react context

You just render the context with your component.

const addItem = jest.fn()
render(
  <AppContext.Provider value={{ addItem }}>
    <MyComponent />
  </AppContext.Provider>
)

See Mocking context with react-testing-library

I want to add a complete test example by using the solution from @Giorgio. Here we are testing that MyComponent is rendered and that its button will be clicked once.

MyComponent.test.js

import React from 'react'
import { render, fireEvent } from 'react-testing-library'

test('component handles button click', () => {
  const addItem = jest.fn()
  render(
    <AppContext.Provider value={{ addItem }}>
      <MyComponent />
    </AppContext.Provider>
  )
  fireEvent.click(screen.getByText(/click me/))
  expect(addItem).toHaveBeenCalledTimes(1)
}