ExpenseForm.test.js

import React from 'react';
import { shallow } from 'enzyme';
import ExpenseForm from '../../components/ExpenseForm.js';
import expenses from '../fixtures/expenses';

test('should render ExpenseForm correctly', () => {
    const wrapper = shallow(<ExpenseForm />);
    expect(wrapper).toMatchSnapshot();
});

test('should render ExpenseForm correctly with expense data', () => {
    const wrapper = shallow(<ExpenseForm expense={expenses[1]}/>);
    expect(wrapper).toMatchSnapshot();
})

test('should render error for invalid form submission', () => {
    const wrapper = shallow(<ExpenseForm />);
    wrapper.find('form').simulate('submit', {
        preventDefault: () => { }
    });
    expect(wrapper.state('errorState')).length.toBeGreaterThan(0); // I named my property errorState
});