使用Mocha进行测试也会启动主程序

Question

I'm trying to use Mocha to test a CLI app. The tests are running fine but, when I launch the testing procedure, it also launches the main app:

$ npm run test

> standardize-js@0.2.2 test C:\Users\Gaspard\Documents\Code\standardize-js
> mocha "./source/**/*.spec.js"

? Choose your project language or framework (Use arrow keys) //<-- THIS IS THE PROGRAM
> Javascript 
  Typescript 
  AngularJS 

  Main function //<-- THIS IS THE TEST
    ask if the configuration is valid
Configuration is not valid, terminating program.
      √ should return false if the configuration is not accepted


  1 passing (29ms)

I'm kind of new to the testing world and I'm really struggling to understand what I'm doing wrong.
Here is the NPM script used to launch mocha :

"test": "mocha \"./source/**/*.spec.js\""

Here is my testing method:

/* eslint-disable func-names */
const { expect } = require("chai");

const main = require("./index").test;

describe("Main function", function() {
  describe("ask if the configuration is valid", function() {
    it("should return false if the configuration is not accepted", function() {
      const fakeAnswer = false;

      expect(main.validateConfiguration(fakeAnswer)).to.equal(false);
    });
  });
});

And here is my index.js file:

function validateConfiguration(answer) {
  if (answer === false) {
    console.log(chalk.red("Configuration is not valid, terminating program."));
    return false;
  }
  return true;
}

const run = async () => {
//MAIN FUNCTION
};

run();

// Export functions and variables to be able to test
exports.test = {
  validateConfiguration
};

Answer 1

It's not a problem with mocha. It is simply now node.js modules work.

When you do this:

const main = require("./index").test;

Node.js will execute index.js and then check the value of module.exports . If the module ( index.js ) sets or modifies module.exports then node will export it for use by require() . But note, in order for node to know that the module has exported anything it must execute the javascript file.

Node.js does not have any ability to parse and analyze javascript syntax (that's V8's job). Unlike other languages such as C or Java, modules in node.js are not implemented at the syntax level. Therefore the javascript language does not need to be modified (eg. ES6 modules) for node.js to support modules. Modules are simply implemented as a design pattern.

In your index.js file you call run:

run();

When require() loads index.js it will therefore also cause run() to be called.

---

Test libraries, not main

The solution to this is to implement your own logic as modules and test that, not test index.js :

mylib.js :

function validateConfiguration(answer) {
  if (answer === false) {
    console.log(chalk.red("Configuration is not valid, terminating program."));
    return false;
  }
  return true;
}

// Export functions and variables to be able to test
exports.test = { validateConfiguration };

index.js :

const validateConfiguration = require("./mylib").test;

const run = async () => {
    //MAIN FUNCTION
};

run();

You can now use your test script as written.

How can you not test code??

The strategy to keep index.js bug free without testing is to remove all logic from it except for the minimum amount of code to wire all your other code up together to run the app. The code should be as simple as "Hello World". That way, the code in main is so small and so simple that you can test it for bugs using your eyeballs.

Any code in index.js that causes a bug should be refactored into its own library so that it can be tested separately. There are a small handful of corner cases, such as loading environment variables or opening port 80 where you can't really separate into a library because they literally are wiring logic. For such cases you just have to be really careful.

Answer 2

之所以称其为run是因为您在定义方法后立即告诉它。