NameScreen.test.js

import 'react-native';
import React from 'react';
import NameScreen from '../NameScreen';
import configureStore from 'redux-mock-store';

import { shallow, configure } from 'enzyme';
import Adapter from 'enzyme-adapter-react-16';

configure({ adapter: new Adapter() });

const mockStore = configureStore();

const initialState = {
  form: {
    fields: {},
    values: {},
  },
  nav: {
    index: 1,
    routes: [],
  },
};

describe('It ', () => {
  test('should render correctly ', () => {
    const props = {
      navigation: jest.fn(),
      onPress: jest.fn(),
    };
    const wrapper = shallow(<NameScreen {...props} />);
    const render = wrapper.dive();
    expect(render).toMatchSnapshot();
  });
  test('should have defined handleOnPress method ', () => {
    const props = {
      navigation: jest.fn(),
      onPress: jest.fn(),
      handleOnPress: jest.fn(),
    };
    const wrapper = shallow(<NameScreen {...props} />);
    const instance = wrapper.instance();
    expect(instance).toHaveProperty('handleOnPress');
    expect(wrapper).toMatchSnapshot();
  });
  test('it should fire the handleOnPress method', () => {
    const props = {
      navigation: {
        navigate: jest.fn(),
      },
      onPress: jest.fn(),
      handleOnPress: jest.fn(),
    };
    const wrapper = shallow(<NameScreen {...props} />);
    const render = wrapper.dive();
    const spyOnHandle = jest.spyOn(wrapper.instance(), 'handleOnPress');
    expect(render).toMatchSnapshot();
    expect(render
      .find('ReduxForm')
      .props()
      .handleOnPress());
    expect(spyOnHandle).toHaveBeenCalled();
  });
});