LanguageSelector.test.js

import React from 'react';
import Enzyme, { mount } from 'enzyme';

// ensure you're resetting modules before each test
beforeEach(() => {
  jest.resetModules();
});

// Takes the context data we want to test, or uses defaults
const getLanguageSelectorWithContext = (context = {languages: ['en', 'fr', 'es'], activeLanguage: 'en'}) => {
  
  // Will then mock the LocalizeContext module being used in our LanguageSelector component
  jest.doMock('./LocalizeContext', () => {
    return {
      LocalizeContext: {
        Consumer: (props) => props.children(context)
      }
    }
  });
  
  // you need to re-require after calling jest.doMock.
  // return the updated LanguageSelector module that now includes the mocked context
  return require('./LanguageSelector').LanguageSelector;
};

describe('<LanguageSelector />', () => {
  it('should return default list of languages', () => {
    // This will use the default context param since we pass nothing
    const LanguageSelector = getLanguageSelectorWithContext();
    const wrapper = mount(<LanguageSelector />);
    expect(wrapper.find('li').length).toBe(3);
  });
  
  it('should render no languages', () => {
    // Here we override the context with the values we want for this specific test
    const LanguageSelector = getLanguageSelectorWithContext({languages: [], activeLanguage: null});
    const wrapper = mount(<LanguageSelector />);
    expect(wrapper.find('li').length).toBe(0);
  });
});