How do I properly test for a rejected promise using Jest?

Question

Code

import { createUser } from '../services'; ... ...  handleFormSubmit = () => {     this.setState({ loading: true });   createUser()     .then(() => {       this.setState({         loading: false,       });     })     .catch(e => {        this.setState({          error: e,        });     }); }; 

Test

 it('rejects...', () => {     const Container = createUserContainer(CreateUser);     const wrapper = shallow(<Container />);        return wrapper.instance().handleFormSubmit()       .catch(e => {          console.log("State: ", wrapper.state());          expect(e).toEqual('error');       });  }); 

Mock

export const createUser = function() {   return new Promise((resolve, reject) => {     reject('error');   }); }; 

The test does force the code to go into the catch in the method. So the state does get set to 'error'.

But in my test, it doesn't do what I expect and wait for the Promise to reject before it tests for the state change. I'm not sure what to try here, should I be using async/await?

So it's the createUser method I want to wait for but I'm not sure my implementation allows for this.

Answer 1

You should do something like this:

it('rejects...', () => {   const Container = createUserContainer(CreateUser);   const wrapper = shallow(<Container />);     return expect(wrapper.instance().handleFormSubmit()).rejects.toEqual('error'); }); 

I think it is cleaner this way. You can see this approach in the official docs.