Jest: spy axios in React

I'm new to Jest (and testing javascript in general). I've got a Register component which is basically a page to register a user. When the form is completed and the submit button is clicked it will use axios to send a POST request to the server.

I'm trying to write the test for this functionality. To do so I need to mock axios. I wrote the following test but when asserting that axios was called I'm getting an error:

 expect(jest.fn()).toHaveBeenCalled()

Expected number of calls: >= 1
Received number of calls:    0

Here's my test:

jest.mock('axios')

it('should save value when submitted', async () => {

            render(
                <Register />
            );

            ReactTestUtils.Simulate.change(field('email'), {
                target: { value: 'test@mail.com', name: 'email'}
            })

            ReactTestUtils.Simulate.change(field('first-name'), {
                target: { value: 'test', name: 'first-name'}
            })

            ReactTestUtils.Simulate.change(field('last-name'), {
                target: { value: 'test', name: 'last-name'}
            })

            ReactTestUtils.Simulate.change(field('password'), {
                target: { value: 'test', name: 'password'}
            })

            ReactTestUtils.Simulate.change(field('confirm-password'), {
                target: { value: 'test', name: 'confirm-password'}
            })


            const postSpy = jest.spyOn(axios, 'post')

            ReactTestUtils.Simulate.submit(form('register'));

            expect(postSpy).toHaveBeenCalled();

        });

Basically I'm populating all the required fields from my form and then submitting it.

The function that handles submission in my Register component looks like this:

const onSubmit = data => {
        const res = axios.post("http://localhost/register", data);
    }

Any idea what am I missing or doing wrong?

Thanks