Generate coverage without made test

[cesco69]

Hi, I have a webserver made with Express.js and I want check the coverage of some request made with Postman, but nyc don't show any line as reached by the requests.

I have made a small reprocucible example:

File structure

├── package.json
├── .nycrc.json
└── index.js

Files

package.json

{
  "name": "test",
  "version": "1.0.0",
  "main": "index.js",
  "scripts": {
    "cover": "nyc node index.js",
  },
  "author": "",
  "license": "ISC",
  "description": "",
  "dependencies": {
    "express": "^5.1.0"
  },
  "devDependencies": {
    "nyc": "^17.1.0"
  }
}

.nycrc.json

{
    "all": true,
    "check-coverage": false,
    "extension": [
        ".js"
    ],
    "include": [
        "**/*.js"
    ],
    "reporter": [
        "text",
        "lcov",
        "html"
    ]
}

index.js

import express from 'express';

const app = express();

app.get('/', (req, res) => {
    res.status(200).send('Hello World');
});

app.listen(3000, () => {
    console.log('Server started on: http://localhost:3000/');
});

Steps to reproduce

1. start the web server:

npm run cover

> test@1.0.0 cover
> nyc node index.js

Server started on: http://localhost:3000/

2. open http://localhost:3000/ in a browser. output:

Hello World

3. close the terminal with CTRL + C, this is the final nyc output:

----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
----------|---------|----------|---------|---------|-------------------
All files |       0 |      100 |       0 |       0 |                  
 index.js |       0 |      100 |       0 |       0 | 3-10             
----------|---------|----------|---------|---------|-------------------

The workaround I have found is manually trigger at runtime the coverage by calling an api /write-coverage:

write-coverage.js

import { mkdirSync } from 'fs';
import { join } from 'path';

export const writeCoverage = async () => {
    const coverage = (global as any).__coverage__;
    if (!coverage) {
        return false;
    }

    const mIstanbulLibReporter = await import('istanbul-lib-report');
    const mIstanbulLibCoverage = await import('istanbul-lib-coverage');
    const mIstanbulReports = await import('istanbul-reports');

    const { createContext } = mIstanbulLibReporter.default;
    const { createCoverageMap } = mIstanbulLibCoverage.default;
    const { create } = mIstanbulReports.default;

    const coverageMap = createCoverageMap(coverage);

    const dir = join(process.cwd(), 'my-coverage');
    mkdirSync(dir, { recursive: true });

    const context = createContext({ dir, coverageMap });
    const report = create('html'); // html, json, text, etc.
    report.execute(context, coverageMap);

    console.log('Coverage:' + dir);
    return true;
};

index.js

import express from 'express';
import { writeCoverage } from './write-coverage.js'

const app = express();

app.get('/', (req, res) => {
    res.status(200).send('Hello World');
});

app.get('/write-coverage', async(req, res) => {
    res.status(200).send(await writeCoverage());
});

app.listen(3000, () => {
    console.log('Server started on: http://localhost:3000/');
});