assigning mock functions on `import *` with flowjs

Question

Say I have the following code:

export const exampleFunc = () => {}

Which is then used in a test like so:

import * as exampleAll from '../../path/to/example'


describe('Example', () => {

  exampleAll.exampleFunc = jest.fn()
})

This fails to typecheck with:

Cannot assign jest.fn() to exampleAll.exampleFunc because property exampleFunc is not writable.

 44│ const mockStore = configureStore([reduxThunk])
 45│
 46│ describe('[Redux action] ExampleAction()', () => {
 47│     exampleAll.exampleFunc = jest.fn()
 48│     beforeEach(() => {
 49│       exampleAll.exampleFunc.mockReturnValue(() => () => {})
 50│     })

Why is it not writable? And how can I do such mocking while also using flow?

Thanks!