Mocking globals in Jest.

log-message.js

function logMessage(message) {
  console.log(message);
}

module.exports = logMessage

log-message.test.js

const logMessage = require('./log-message.js');
const console = global.console;

test('Should call console.log', () => {
  const logMock = jest.fn();

  Object.defineProperty(global.console, 'log', {
    value: logMock
  });

  logMessage('Hello World!');
  expect(logMock).toBeCalledWith('Hello World!');
});

afterEach(() => {
  global.console = console;
});