React-Jest : axios.get.mockRejectedValue doesnt respect async-await - reactjs

Question

I am using jest and enzyme for Unit Testing of a React App created using create-react-app. I have an axios call and I call other functions like myfunction.onSuccess() and myfunction.onError() from another component on success and error of the axios call respectively. I have put an assert to expect(myfunction.onSuccess).toHaveBeenCalledTimes(1); This works fine for mockResolvedValue but not for mockRejectedValue. I see that async-await is not respected for mockRejectedValue.
I have created a sample code and used window.alert as the function to be called in both then and catch block to keep it simple here and expecting this function to be called once as an assert. Why is there a difference and how to tackle this?
Async.js
import React from 'react';
import axios from 'axios';
class Async extends React.Component {
constructor(props) {
super(props);
this.state = {
posts: []
};
}
getAllPosts() {
axios.get(`https://jsonplaceholder.typicode.com/posts`)
.then(response => {
if (response.data) {
this.setState({ posts: response.data });
window.alert("Data fetch Success");
}
}).catch(error => {
window.alert(error.message);
});
}
render() {
return (
<div>
<button onClick={() => { this.getAllPosts() }}>Fetch Posts</button>
<ul>
{this.state.posts.map((post) => (
<li key={post.id}>{post.title}</li>
))}
</ul>
</div>
);
}
}
export default Async;
Async.test.js
import React from 'react';
import Async from './Async';
import { shallow } from 'enzyme';
import axios from "axios";
jest.mock("axios");
describe('Async Component', () => {
const wrapper = shallow(<Async />);
const layout = wrapper.instance();
it('to notify success when posts', async () => {
window.alert = jest.fn();
const response = { data: [{ id: '1', title: 'something' }, { id: '2', title: 'something else' }] };
axios.get.mockResolvedValue(response);
await layout.getAllPosts();
expect(layout.state.posts).not.toBe([])
expect(window.alert).toHaveBeenCalledTimes(1);
});
it('to notify failure when error is encountered', async () => {
window.alert = jest.fn();
const error = { message: '500 Internal Server Error' };
axios.get.mockRejectedValue(error);
await layout.getAllPosts();
expect(window.alert).toHaveBeenCalledTimes(1); // why doesn't this work?
});
});