CI/CD: Error: ECONNREFUSED: Connection refused

I have a nodejs, express api built using typescript and a mongo database.

I am using mocha, chai and supertest to write my tests. Although they work locally they are all failing when they go through the test job. The pipeline fails on the test stage. Giving the following error: ECONNREFUSED: Connection refused.

gitlab-ci.yml

stages:
  - quality
  - test
  - build
  - deploy
  
image: node:8.11.3

services:
  - mongo
  
before_script:
- npm install

quality:
  stage: quality
  script:
  - npm run-script lint
  
test:
  stage: test
  script:
  - npm run-script test

build:
  stage: build
  script:
  - npm run-script build
  
deploy:
    stage: deploy
    script:
    - echo "TODO deploy"

tests

    import { assert, expect } from "chai";
    import request from "supertest";
    import app from "./../src/index";
    
    describe("Authentication", () => {
    
        it("should respond with 200 product_id is authorised", async () => {
    
            const result = await request(app).post("/api/auth")
                .send({
                    product_id: "123",
                })
                .expect("Content-Type", /json/)
                .expect(200);
    
        });
    
        it("should respond with session token", async () => {
    
            const result = await request(app).post("/api/auth")
                .send({
                    product_id: "123",
                });
    
            expect(result.body.data).to.have.property("token");
    
        });
    });

package.json

    "test": "mocha -r ts-node/register --project tsconfig.json test/*.test.ts --exit"

errors:

    > mocha -r ts-node/register --project tsconfig.json test/*.test.ts --exit
    
    Server Running On: runner-sefsf-project-41-concurrent-0gdrs7:3000
    
    
      Authentication
    MongoDB Successfully Connected On: mongodb://localhost:27017/paycasso
        1) should respond with 200 product_id is authorised
        2) should respond with session token
    
      Server
        3) should be up
        4) should throw 404 for unrecognized routes
    
      Transaction
        5) should respond with a new transction
    
    
      0 passing (40ms)
      5 failing
    
      1) Authentication
           should respond with 200 product_id is authorised:
         Error: ECONNREFUSED: Connection refused
          at Test.assert (node_modules/supertest/lib/test.js:165:15)
          at assert (node_modules/supertest/lib/test.js:131:12)
          at /eng/paycasso-server/node_modules/supertest/lib/test.js:128:5
          at Test.Request.callback (node_modules/superagent/lib/node/index.js:718:3)
          at ClientRequest.req.once.err (node_modules/superagent/lib/node/index.js:646:10)
          at Socket.socketErrorListener (_http_client.js:382:9)
          at emitErrorNT (internal/streams/destroy.js:82:8)
          at emitErrorAndCloseNT (internal/streams/destroy.js:50:3)
          at process._tickCallback (internal/process/next_tick.js:63:19)
    
      2) Authentication
           should respond with paycasso session token:
         Error: ECONNREFUSED: Connection refused
          at Test.assert (node_modules/supertest/lib/test.js:165:15)
          at assert (node_modules/supertest/lib/test.js:131:12)
          at /eng/paycasso-server/node_modules/supertest/lib/test.js:128:5
          at Test.Request.callback (node_modules/superagent/lib/node/index.js:718:3)
          at ClientRequest.req.once.err (node_modules/superagent/lib/node/index.js:646:10)
          at Socket.socketErrorListener (_http_client.js:382:9)
          at emitErrorNT (internal/streams/destroy.js:82:8)
          at emitErrorAndCloseNT (internal/streams/destroy.js:50:3)
          at process._tickCallback (internal/process/next_tick.js:63:19)

Apparently the connection is being refused? But i'm not sure what it means by this specifically because you can see the server in the error log is connected and so is the mongo service.

index.ts

    import Server from "./server";
    
    export default new Server().server;

server.ts

import App from "./app";

    class Server {
    
        public server: any;
        private instance: any;
        private app: any;
        private config: any;
    
        constructor() {
    
            this.instance = new App();
            this.app = this.instance.app;
            this.config = this.instance.config;
            this.server = this.app.listen(this.config.port, this.config.hostname);
    
            console.log("Server Running On: " + this.config.hostname + ":" + this.config.port);
    
        }
    
    }
    
    export default Server;