ES Modulesで「プライベートメソッドをテストする」をやりたいとき

functions.js

export function publicFunction() {

}

function complexPrivateFunctionA() {
  
}

function complexPrivateFunctionB() {
  
}

function complexPrivateFunctionC() {
  
}

export const __dangerousExportForTesting = {
  complexPrivateFunctionA,
  complexPrivateFunctionB,
  complexPrivateFunctionC,
};

functions.test.js

import {
  publicFunction,
  __dangerousExportForTesting,
} from './functions';

describe('publicFunction', () => {
  test('hoge', () => {
    publicFunction();
  });
});

describe('complexPrivateFunctionA', () => {
  const { complexPrivateFunctionA } = __dangerousExportForTesting;
  test('hoge', () => {
    complexPrivateFunctionA();
  });
});

describe('complexPrivateFunctionB', () => {
  const { complexPrivateFunctionB } = __dangerousExportForTesting;
  test('hoge', () => {
    complexPrivateFunctionB();
  });
});

describe('complexPrivateFunctionC', () => {
  const { complexPrivateFunctionC } = __dangerousExportForTesting;
  test('hoge', () => {
    complexPrivateFunctionC();
  });
});