Mock not being called in Jest - unit-testing

Question

Please help me understand Jest mocks.
I've put some dummy functions in a file:
// actions.js
export function f1() {
return 1
}
export function calls_f1() {
f1()
}
And then in my test file I'm trying to understand how to check that a function calls another function:
import * as actions from './actions.js'
describe("MOCKS", () => {
actions.f1 = jest.fn();
actions.calls_f1();
expect(actions.f1).toBeCalled();
});
But the test is failing saying the mock function wasn't called. I've also tried swapping the 2nd and 3rd lines of the test, to no avail.
My jest config is all good, I've actually been doing a bunch of other testing (in this same file) that works.
What am I missing here?
Note: The actual implementation of this (that I'm simplifying greatly here) involves an actions file that includes a public export function fetchStations() that calls a private (or, rather, not exported) export function _downloadStations(). I'm trying to test that _downloadStations() is called.
I'm using import * as actions only for convenience, so I can write that line and then use whatever functions that file exports under actions.whatever() (instead of having to add functions to the import statement when I decide to use them). If import * as actions has some effect I'm not noticing (as implied by brian below) then I certainly don't have to use it and can use import {thisAction, thatAction} from './actions' of course.

Answer 1

This line:
import * as actions from './actions.js'
binds the module exports from actions.js to actions...
...so setting actions.f1 to a mock function replaces the module export for f1...
...but this doesn't affect calls_f1 since it calls f1 directly.
If calls_f1 is changed to call the module export for f1 then it will call the mock function.
There are two ways to make that happen.
One way is to move f1 into its own module.
The other way is to note that ES6 modules "support cyclic dependencies automatically" (a major design goal of ES6 modules) so a module can import its own exports:
actions.js
import * as actions from './actions'; // <= import the module...
export function f1() {
return 1
}
export function calls_f1() {
actions.f1() // <= ...and use it to call f1
}
actions.test.js
import * as actions from './actions.js'
describe('actions', () => {
it('calls_f1 should call f1', () => {
actions.f1 = jest.fn();
actions.calls_f1();
expect(actions.f1).toBeCalled(); // Success!
})
})
Update
OP updated the question to indicate that the function in question is not exported from the module.
In that case it is just an internal implementation detail of the module and cannot be spied on directly.
Testing it would involve testing for the effects that it causes, and not directly spying on it to see if it was called.