Extending supertest in Typescript

Question

I'm trying to create a extension on supertest.

Using what I found in question Extending SuperTest. I have this working example on javascript:

const request = require('supertest');
const Test = request.Test;

Test.prototype.authenticate = function(user) {
  const {token, xsrfToken} = user.tokens;

  return this
   .set('Authorization', `Bearer ${token}`)
   .set('X-XSRF-TOKEN', xsrfToken);
}

And inside a test block I can use:

request(app)
  .post('/user/settings')
  .authenticate(user)
  .send(...)

This works fine. The problem now is to use the extension in a *.test.ts file.

As suggested in Extend Express Request object using Typescript, I try to create a file to use the typescript feature Declaration Merging.

// file location: ./src/types/supertest

declare namespace supertest {
  export interface Test {
    authenticate(user: any): this; // I didn't put a type on user to simplify here.
  }
}

and also changed my tsconfig.json

{
  "compilerOptions": {

    ...

    "typeRoots": ["./src/types"],

    ...

  }
}

But when I run npx tsc

$ npx tsc
src/api/user.test.ts:51:8 - error TS2551: Property 'authenticate' does not exist on type 'Test'.

51       .authenticate(user);
          ~~~~~~~

Question
Is there a way to fix this on typescript environment?

[EDIT]
Extra Information (not necessarily useful):
In the same project I have extensions on express, chai and pdf-merge-js. All of them works fine using the approach described above.

There is something peculiar about supertest maybe about @types/supertest that is preventing it to work.

This is a little bit of the code in my project that already work's for express:

// file location: ./src/types/express
import { ModelBase } from '../../models/base';

declare global {
  namespace Express {
    export interface Response {
      model: (model: ModelBase) => this;
    }
  }
}

Answer 1

I'm not sure why, but this worked for me:

declare module "supertest" {
  interface Test extends superagent.SuperAgentRequest {
    authenticate(user: any): this;
  }
}

Structure:

index.ts
tsconfig.json
types
  - supertest
    - index.d.ts

My index.ts:

import request from "supertest";
import express from "express";

const app = express();

app.get("/user", function (req, res) {
  res.status(200).json({ name: "john" });
});

request(app)
  .post("/user/settings")
  .authenticate({ tokens: { token: "", xsrfToken: "" } })
  .send();

My tsconfig.json:

{
  "compilerOptions": {
    "outDir": "dist",
    "rootDir": ".",
    "typeRoots": ["./types", "./node_modules/@types"],
    "esModuleInterop": true
  },
  "files": ["./types/supertest/index.d.ts", "index.ts"]
}

My types/supertest/index.d.ts:

import superagent from "superagent";

declare module "supertest" {
  interface Test extends superagent.SuperAgentRequest {
    authenticate(user: any): this;
  }
}

I think that declare module "supertest" is the key part. Everything else you got right.