Testing an async Redux action call

I have the following async call in one of my React components:

onSubmit = (data) => {
    this.props.startAddPost(data)
        .then(() => {
            this.props.history.push('/');
        });
};

The goal here is to redirect the user to the index page only once the post has been persisted in Redux (startAddPost is an async action generator that sends the data to an external API using axios and dispatches another action that will save the new post in Redux store; the whole thing is returned, so that I can chain a then call to it in the component itself). It works in the app just fine, but I'm having trouble testing it.

import React from 'react';
import { shallow } from 'enzyme';

import { AddPost } from '../../components/AddPost';
import posts from '../fixtures/posts';

let startAddPost, history, wrapper;

beforeEach(() => {
    startAddPost = jest.fn();
    history      = { push: jest.fn() };
    wrapper      = shallow(<AddPost startAddPost={startAddPost} history={history} />);
});

test('handles the onSubmit call correctly', () => {
    wrapper.find('PostForm').prop('onSubmit')(posts[0]);

    expect(startAddPost).toHaveBeenLastCalledWith(posts[0]);
    expect(history.push).toHaveBeenLastCalledWith('/');
});

So I obviously need this test to pass, but it fails with the following output:

● handles the onSubmit call correctly

TypeError: Cannot read property 'then' of undefined

at AddPost._this.onSubmit (src/components/AddPost.js:9:37)
at Object.<anonymous> (src/tests/components/AddPost.test.js:25:46)
at process._tickCallback (internal/process/next_tick.js:109:7)

So how can I fix this? I suspect this is a problem with the test itself because everything works well in the actual app. Thank you!