Running a local server and API testing in less than 10 minutes

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Written by - Millan Kaul

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Time is money 💲

So in next 10 minutes or less 🤞 I promise, we will:

1. Start an API server on your machine (localhost)
2. Run independent API test on server.
   • Test’s include assertion

✔️ All this without using any dependency !!! ✔

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+                      Time starts now ⏱️

Fig.1 - 10 minute timer

Step 1 : Set up the node / NodeJS

💡 Think of NodeJs like JVM if you are familiar with java

If you already have it setup then you can jump to Code and run

Go to nodejs.org and download / install NodeJs on your platform. You may also Check their official Releases page

macos users : brew install node linux users : sudo apt install node

Check installation by running this node -v on your terminal / cmd and you will see :

node -v
v16.8.0

Version 16 was the latest while writing this article.

☑️ And that’s all you need today in terms of setup

Run and Test in 4 simple steps

1️⃣ Setup server ✔️

2️⃣ Run server 🏃🎽

3️⃣ Write tests 📝

4️⃣ Run API test’s 🚀

To keep it simple, we will keep server and test files in the same folder/directory.

So lets create a folder named dev on Desktop

Desktop/dev

Let’s Start !

1️⃣ Setup server✔️

Go to dev folder (cd Desktop/dev) and create a file named server.js and copy this code:

//server.js

const http = require("http");

const HOST = "localhost";
const PORT = 8020;

const server = http.createServer(async (req, res) => {
console.log("Request on server received :  " + req.method + " : " + req.url);

  /**
   * Health check endpoint `/health`
   * 
   * @path {HOST}:{PORT}/health
   * @return status : {200}
   * @return message : text : "If you see this message, your API server is all set , Welcome !"
   */
  if (req.url === "/" && req.method === "GET") {
    // set the status code, and content-type
    res.writeHead(200, { "Content-Type": "application/json" });
    // send the response data as text
    res.end("If you see this message, your API server is all set , Welcome !");
  } 


  /**
   * Health check endpoint `/health`
   * 
   * @path {HOST}:{PORT}/health
   * @return status {200:OK}
   * @return uptime : how long has been server up & running
   * @return timestamp : Time of response from server  
   */
  else if (req.url === "/health" && req.method === "GET") {
    const healthcheck = {
      uptime: process.uptime(),
      message: "OK",
      timestamp: Date.now(),
    };
    res.end(JSON.stringify(healthcheck));
  } 

  
  /**
   * Endpoint not implemented / invalid endpoint
   * @path {optional} `/`
   * @return {404} - Route is not implemented (Page Not Found)
   */
  else {
    res.writeHead(404, { "Content-Type": "application/json" });
    res.end(
      JSON.stringify({ message: "Route is not implemented" })
    );
  }
});

server.listen(PORT, () => {
  console.log(`server started on : ${HOST}  port: ${PORT}`);
});

So we created a javaScript file to set up a local server that we will run (in next step).

In same file we created 2 endpoints:

http://localhost:8020/        //Base url : GET Home Page
http://localhost:8020/health  //Health   : GET server status

2️⃣ Run server🏃🎽

Open your terminal/cmd and navigate to Desktop/dev

cd ~/Desktop/dev 

and run your server using this command:

node server.js

If you see this message, it means your API Server is all set !

Fig.2 - server started on http://localhost:8020

You can even check it on your browser:

Fig2.1 - server ( http://localhost:8020) accessible on browser

3️⃣ Write tests 📝

Under same folder Desktop/dev now create a file named test.js and copy this code:

//test.js

const http = require('http');
const assert  = require("assert");

let BASE_URL = "http://localhost:8020";


  /**
   * Test 1 : Hit BASE_URL and assert response statusCode to be  === 200
   * 
   * @path {BASE_URL}
   * @return expect : {200}
   */
http.get(BASE_URL, (response) => {
      console.log("Response: " + response.statusCode);
      assert(response.statusCode === 200);
    });

  /**
   * Test 2 : Hit `/health` endpoint and assert response statusCode to be  === 200
   * 
   * @path {BASE_URL}/health
   * @return status : {200}
   */
http.get(BASE_URL+'/health', (response) => {
      console.log("Response: " + response.statusCode);
      assert(response.statusCode === 200);
    });


  /**
   * Test 3 : Hit random endpoint `/thisIsNotAValidEndpoint` and assert response statusCode to be  === 404
   * 
   * @path {BASE_URL}/thisIsNotAValidEndpoint
   * @return status : {404}
   */
http.get(BASE_URL+'/thisIsNotAValidEndpoint', (response) => {
      console.log("Response: " + response.statusCode);
      assert(response.statusCode === 200);
    });

4️⃣ Run API test’s 🚀

1. Make sure you open a new terminal/cmd window to run this.
2. Be sure that our server is still running (step 2️⃣ Run server🏃🎽 ) on separate terminal/cmd.

node test.js

you will see something like this:

dev $ node test.js 
Response: 200
Response: 200
Response: 404
node:assert:400
    throw err;
    ^

AssertionError [ERR_ASSERTION]: The expression evaluated to a falsy value:

  assert(response.statusCode === 200)

    at ClientRequest.<anonymous> (.../Desktop/dev/test.js:40:7)
    at Object.onceWrapper (node:events:514:26)
    at ClientRequest.emit (node:events:394:28)
    at HTTPParser.parserOnIncomingClient [as onIncoming] (node:_http_client:621:27)
    at HTTPParser.parserOnHeadersComplete (node:_http_common:128:17)
    at Socket.socketOnData (node:_http_client:487:22)
    at Socket.emit (node:events:394:28)
    at addChunk (node:internal/streams/readable:315:12)
    at readableAddChunk (node:internal/streams/readable:289:9)
    at Socket.Readable.push (node:internal/streams/readable:228:10) {
  generatedMessage: true,
  code: 'ERR_ASSERTION',
  actual: false,
  expected: true,
  operator: '=='
}

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WHAT ❗ ❗

What just happened ❓ , why all these logs are printed.

Don’t panic, it was expected, here is why ⬇️

In the above test.js this was intentionally put to demo, what will happen when an test fails on assertion.

Troubleshooting : Start by reading error printed:

AssertionError [ERR_ASSERTION]: The expression evaluated to a falsy value:

  assert(response.statusCode === 200)

What it tells is that “the expected response code 200 was not received”.

Question : But which one ❓

Answer : Read just 1 more line from logs it tells you exactly where test.js:40:7

 at ClientRequest.<anonymous> (.../Desktop/dev/test.js:40:7)

Let’s Fix this :

• Open test.js in your text editor.
• Go to line # 40

assert(response.statusCode === 200);

Change 200 to 404

assert(response.statusCode === 404);

now save and close this file.

Self assignment: Try to explore the reason yourself. hint: line # 33 of test.js

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Let’s try to run test’s once again 🏃 🚀

node test.js

Done !

Fig.3 - Successful Test run ✔️

Time over :)

Fig.3.1 - Time over

Credits for API icon

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