jest-test-module-preprocessor

This package aims to simplify requiring module file when testing with Jest

Usage

0. Run following command in project root

    npm install --save-dev jest-test-module-preprocessor
   

1. Add following property to your jest config

    {
      "transform": {
        "\\.js$": "<rootDir>/jest/transform.js"
      }
    }
   

2. Put following code in jest/transform.js

    const preprocessor = require('jest-test-module-preprocessor')();
   
    module.exports = {
      process: (...args) => {
        const transformed = preprocessor.process(...args);
        return transformed;
      },
    };
   

3. Then you can simplify require the module you intrested when writing test file

    // In <rootDir>/test/a/b/c/d.spec.js
    const d = require('__module__');
   
    // The above statement is same as
    // require('../../../../src/a/b/c/d.js');
   

Configuration

When initializing preprocessor, an optional configuration can be used.

const preprocessor = require('jest-test-module-preprocessor')({
  modulePlaceholder: '__module__',
  srcDir: 'src'
});

Notes about babel-jest

When "transform" is overwritten in any way the babel-jest is not loaded automatically anymore

In order to utilize babel-jest, modify jest/transform.js as following:

const preprocessor = require('jest-test-module-preprocessor')();

const babel = require('babel-jest');

module.exports = Object.assign(
  {},
  babel,
  {
    process: (...args) => {
      const transformed = preprocessor.process(...args);
      const code = babel.process(
        transformed,
        ...args.slice(1)
      );
      return code;
    },
  }
);