Postman is one of the popular tools to make API requests. It allows to user to work with HTTP, GraphQL, WebSocket, <a href="http://Socket.IO">Socket.IO</a>, MCP, etc. We are going to cover Postman&rsquo;s Pre-request and Post-response (tests) scripts for Restful API (HTTP). With Postman, it has been very much easier to make HTTP requests. Most developers also use it to test the APIs in dev stage or verify the production APIs. Sometimes, we might miss out on the details for testing or verifying. This is where HTTP pre-requests and post-response scripts come into play. Basic breakdown:
<ol>
<li style="font-size: 14pt;">Pre-request script:
<ul style="list-style-type: disc;">
<li style="font-size: 14pt;">JS script that is run before API request</li>
<li style="font-size: 14pt;">helpful when we need to inject a dynamic value in the request body, header or params. </li>
</ul>
</li>
<li style="font-size: 14pt;">Post-response script (test):
<ul style="list-style-type: disc;">
<li style="font-size: 14pt;">JS script that is run after getting the API response</li>
<li style="font-size: 14pt;">helpful to test if the response is valid. This can be valid status code, valid response body, desired response header, etc. </li>
</ul>
</li>
</ol>
Let's see how it's done in visuals. For this test example, I've used a <a href="https://dummyjson.com/">DummyJson - Free Fake REST API</a>. 
Here, I will cover:
<ol>
<li style="font-size: 14pt;">
<h3>Login: </h3>
- Inject dynamic value in the request body using Pre-request script&nbsp; - Test if the response is success and automatically set environment variable using post-response script. </li>
<li style="font-size: 14pt;">
<h3>Get current user: </h3>
- Get current user using the derived access token from login - Test and validate the response as per our need </li>
</ol>
Login 
<ul>
<li style="list-style-type: none;">
<ul style="list-style-type: disc;">
<li style="font-size: 14pt;">Pre-request Script 
<pre class="language-javascript" style="font-size: 11pt;"><code>// Payload body:

{
 "username": "emilys",
 "password": "emilyspass",
 "expiresInMins": {{expiresIn}} // dynamic variable we will be injecting using Pre-request script
}

// Pre-request script. Click on Scripts &gt; Pre-request (on the left panel)

pm.environment.set("expiresIn", 300);
</code></pre>
&nbsp;
</li>
<li style="font-size: 14pt;">Post-request Script Here, we have tested if the success response has code 200, if the response has accessToken, refreshToken that are not null and gender is female. If any one of the test case fails, the whole test is considered failed. 
<pre class="language-javascript" style="font-size: 11pt;"><code>pm.test("Status code is 200", function () {
 pm.response.to.have.status(200); // test if the response is success and has 200 status code
})

const response = pm.response.json();
pm.test("Necessary tokens are available", function () {
 pm.expect(response.accessToken).to.not.be.null // test that accessToken is not null
 pm.expect(response.refreshToken).to.not.be.null // test that refreshToken is not null
 pm.expect(response.gender).equals('female') // test that gender is female
});

// set environment variables
pm.environment.set("accessToken", response.accessToken);
pm.environment.set("refreshToken", response.refreshToken);
</code></pre>
 When we hit send, we can see something like this:
<img src="../../api/file-read/uploads/1501bd9d76bff64f0ea0c6401" width="1007" height="532"> On clicking the `Test Results` tab: <img src="../../api/file-read/uploads/1501bd9d76bff64f0ea0c6402" width="453" height="233"> </li>
</ul>
</li>
</ul>
<h3>Get current user </h3>
<ul>
<li style="list-style-type: none;">
<ul style="list-style-type: disc;">
<li style="font-size: 14pt;">Set access token as bearer token: The value of the&nbsp;accessToken is set from the post-response script used in login.&nbsp; <img src="../../api/file-read/uploads/1501bd9d76bff64f0ea0c6403" width="1010" height="270"> </li>
<li style="font-size: 14pt;">Post-response script: Here, we have tested if the success response has code&nbsp;200, phone number and date of birth are valid. 
<pre class="language-javascript" style="font-size: 11pt;"><code>pm.test("Status code is 200", function () {
 pm.response.to.have.status(200); // test if the response status is 200
})

const response = pm.response.json();
pm.test("Phone number format is valid", function () {
 const regex = /^\+\d{1,3}\s\d{2,4}-\d{3}-\d{4}$/;
 pm.expect(response.phone).to.match(regex); // phone number validity check using Regex
})

pm.test("Valid DOB", function () {
 const dateFromResponse = new Date(response.birthDate)
 pm.expect(dateFromResponse.getTime()).lessThan((new Date()).getTime()) // D.O.B validity check. Date should be less than today
})</code></pre>
 On sending the request, we should get success response and all the test should also pass. If the test fails, it will show something like below: <img src="../../api/file-read/uploads/1501bd9d76bff64f0ea0c6405" width="1051" height="268"></li>
</ul>
</li>
</ul>

Sometimes, developers might miss out on the details when testing or verifying. This is where HTTP pre-requests and post-response scripts come into play 🔥 

Backend

Working with Postman's HTTP Pre-request and Post-response (test) scripts

Email sending feature is a-must in almost every application. Here is the tutorial on how we can send email using nodemailer and OAuth 2.0 🚀🔥&nbsp; This first step is crucial as we need client ID and client secret which will be later added in the OAuth2 playground to enable mail. First, we need to sign-in to <a href="https://console.cloud.google.com/welcome" target="_blank" rel="noopener">google cloud console</a>. If you have not created a project there, you need to create one and also set up a consent screen.&nbsp; For now, I&rsquo;m assuming we already have that. On the side menu, go to the &ldquo;APIs and services&rdquo; menu and click on &ldquo;Credentials&rdquo;. After that click on &ldquo;CREATE CREDENTIALS&rdquo; in the top-middle section. A dropdown menu will appear. From there, click on OAuth client ID. After that, select the application type you need (for now: Web application) and fill up the name you want. For &ldquo;Authorised redirect URIs&rdquo;, add this URI:&nbsp;<a href="https://developers.google.com/oauthplayground">https://developers.google.com/oauthplayground</a>. This URI is of OAuth 2.0 playground. Now click on &ldquo;CREATE&rdquo;. 
&nbsp;
<img style="display: block; margin-left: auto; margin-right: auto;" src="../../api/file-read/uploads/e50fc64c7971cd4dd64ac1f01" width="832" height="258">
&nbsp;
 Note: the created project might take a few minutes to hours to come into effect.
&nbsp;
Right after creating, we will get client ID and client secret. Now go to <a href="https://developers.google.com/oauthplayground" target="_blank" rel="noopener">OAuth 2.0 playground</a>.&nbsp; &nbsp;
 <img style="display: block; margin-left: auto; margin-right: auto;" src="../../api/file-read/uploads/e50fc64c7971cd4dd64ac1f02" width="796" height="355"> 
On the right top, click on the setting icon. There we will see different options but one we need appears after checking on &ldquo;Use your own OAuth credentials&rdquo;. After checking, input fields with client ID and client secret appear. Paste those credentials we got from google console and close it. After that on the right panel in &ldquo;Step 1&rdquo;, search for &ldquo;Gmail API v1&rdquo; and click on &ldquo;<a href="https://mail.google.com/">https://mail.google.com/</a>&rdquo;. Click on the &ldquo;Authorize APIs&rdquo; button. After success, Step 2 will be active and we can see the Authorization code and exchange button just below it. Click on the button. Now we will get &ldquo;Refresh token&rdquo; and &ldquo;Access token&rdquo;. Okay now let&rsquo;s do some coding 👨&zwj;💻
<ol style="list-style: auto; margin: 16px 0px; padding: 0px 0px 0px 40px;">
<li dir="ltr" style="font-size: 14pt; text-align: left;" aria-level="1">
Create a project Go to your preferred terminal and run: 
<pre class="language-markup" style="font-size: 11pt;"><code>npm init -y</code></pre>
 This command will initialize your node project and create package.json for you. Install necessary packages:&nbsp; 
<pre class="language-markup" style="font-size: 11pt;"><code>npm install nodemailer googleapis</code></pre>
 "googleapis" package is required to authenticate and authorize. 
</li>
<li dir="ltr" style="font-size: 14pt; text-align: left;" aria-level="1">
Create env file and paste the credentials like following:
<pre class="language-markup" style="font-size: 11pt;"><code>GOOGLE_PLAYGROUND_REFRESH_TOKEN=&lt;your refresh token&gt;
GOOGLE_APP_CLIENT_ID=&lt;your client id&gt;
GOOGLE_APP_CLIENT_SECRET=&lt;your client secret&gt;
GOOGLE_PLAYGROUND_REDIRECT_URI=https://developers.google.com/oauthplayground
</code></pre>
&nbsp;
</li>
<li dir="ltr" style="font-size: 14pt; text-align: left;" aria-level="1">
For better read, I&rsquo;ve created a config file:
<pre class="language-javascript" style="font-size: 11pt;"><code>// config.js in root directory

require("dotenv").config();

const GOOGLE_PLAYGROUND_REFRESH_TOKEN =
 process.env.GOOGLE_PLAYGROUND_REFRESH_TOKEN;
const GOOGLE_APP_CLIENT_ID = process.env.GOOGLE_APP_CLIENT_ID;
const GOOGLE_APP_CLIENT_SECRET = process.env.GOOGLE_APP_CLIENT_SECRET;

module.exports = {
 GOOGLE_PLAYGROUND_REFRESH_TOKEN,
 GOOGLE_APP_CLIENT_ID,
 GOOGLE_APP_CLIENT_SECRET,
};
</code></pre>
&nbsp;
</li>
<li dir="ltr" style="font-size: 14pt; text-align: left;" aria-level="1">
Next, I&rsquo;m creating a src/service directory and new file inside service directory From root directory, run the following commands:
<pre class="language-markup" style="font-size: 11pt;"><code>mkdir -p src/service
touch src/service/nodemailer.js</code></pre>
&nbsp;
</li>
<li dir="ltr" style="font-size: 14pt; text-align: left;" aria-level="1">
Open the nodemailer.js file and paste the following code:
<pre class="language-javascript" style="font-size: 11pt;"><code>const nodemailer = require("nodemailer");
const { google } = require("googleapis");

const {
 GOOGLE_PLAYGROUND_REDIRECT_URI,
 GOOGLE_APP_CLIENT_ID,
 GOOGLE_APP_CLIENT_SECRET,
 GOOGLE_PLAYGROUND_REFRESH_TOKEN,
} = require("../config");

async function initiateTransporter(user) {
 try {
 const oAuth2client = new google.auth.OAuth2(
 GOOGLE_APP_CLIENT_ID,
 GOOGLE_APP_CLIENT_SECRET,
 GOOGLE_PLAYGROUND_REDIRECT_URI
 );
 oAuth2client.setCredentials({
 refresh_token: GOOGLE_PLAYGROUND_REFRESH_TOKEN,
 });

 const transporter = nodemailer.createTransport({
 service: "gmail",
 auth: {
 type: "OAuth2",
 user,
 clientId: GOOGLE_APP_CLIENT_ID,
 clientSecret: GOOGLE_APP_CLIENT_SECRET,
 refreshToken: GOOGLE_PLAYGROUND_REFRESH_TOKEN,
 },
 });

 return transporter;
 } catch (err) {
 console.log("Error while initiating transporter");
 console.log(err);
 }
}

module.exports = { initiateTransporter };
</code></pre>
 As you can see here, this code simply authenticates and establishes a connection using googleapis. After that there is the invoke of createTransport() function provided by nodemailer. 
</li>
<li dir="ltr" style="font-size: 14pt; text-align: left;" aria-level="1">
Now create another file or function whose main purpose is to send email. Here I&rsquo;ve created an email.js file at the root directory.
<pre class="language-javascript" style="font-size: 11pt;"><code>const { initiateTransporter } = require("./service/nodemailer");

async function emailInitiate() {
 try {
 const yourEmail = "&lt;Your email address&gt;";
 const transporter = await initiateTransporter(yourEmail);

 await transporter.sendMail({
 from: yourEmail,
 to: "&lt;Email address to whom you want to send email&gt;",
 subject: "Nodemailer with OAuth",
 html: "&lt;p&gt;Hello world&lt;/p&gt;",
 attachments: [], // include if any
 });

 console.log("Email sent");
 } catch (err) {
 console.log("Error while sending email");
 }
}

emailInitiate();</code></pre>
&nbsp;
</li>
<li dir="ltr" style="font-size: 14pt; text-align: left;" aria-level="1">
Now lets run following in your terminal:
<pre class="language-markup" style="font-size: 11pt;"><code>node src/email.js</code></pre>
 Output will be displayed after email is sent successfully:
<pre class="language-markup" style="font-size: 11pt;"><code>Email sent</code></pre>
 Happy coding!! 🙂
</li>
</ol>

Email sending feature is a-must in almost every application. Here is the tutorial on how we can send email using nodemailer and OAuth 2.0 🚀🔥 

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