What is Supertest and why use one?

Supertest is a Node.js library that allows developers and testers to test the APIs. It enables developers and testers to write automated tests for routes and endpoints.

It can be used as a standalone library or with testing frameworks like Mocha and Jest and provides a high-level abstraction to test HTTP requests. This means that in case the developer’s Node.js application is running an HTTP server, they don’t need a running server. Supertest is normally used by testers and developers for writing automated tests for routes and endpoints. It also extends another library called superagent which is a JavaScript client for Node.js and the browser. Usually, SuperTest is used as a standalone library or with popular JavaScript testing frameworks like Mocha and Jest.

Supertest can integrate with other testing frameworks easily with just a few lines of commands by sending a method like GET, PUT, and POST.

Why Use Supertest?

Most modern software use microservices and thus can function only with HTTP APIs that connect the frontend and backend components and third-party APIs for essential features. As mentioned earlier, SuperTest provides a high-level abstraction to test HTTP requests which means that if the  Node.js application is running an HTTP server; a running server is not essential. Requests can be made directly and to test any HTTP requests, just a few lines of commands are required by sending a method like GET, PUT and POST.

How to Get Started with Supertest?

Step 1: Install the Supertest package

Step 2: Create an HTTP request

The first approach tests an external API, or an internal API already deployed and running in the staging environment. All you need to do is provide the URL as a parameter. Use the GET () method. This tells the Supertest to use the HTTP GET verb. Additional methods can be included in the call for setting authentication. Developers and testers can also add custom HTTP headers or body too. Use the END () method to finalize the request and call the API server.

Another approach of creating an HTTP request is useful if the API is built with a Node.js framework. In this case, if necessary, the Supertest starts a test server and sends the requests there. The actual testing will now follow.

Step 3: Set response expectations

Start with setting the expectations for a functional API test. You need to confirm that the API responds as expected. Use the expect () method to extend the superagent. It allows to test several things related to the API response. The HTTP APIs will return with various status codes, such as the 4xx range that indicates an error and the 5xx range that indicates server errors. A successful API request will return with a status code ranging from 200 to 204, depending upon the information available in the API documentation.

Step 4: Check the response bodies

Ensure that the developers and testers don’t just check the HTTP status codes and headers. That would result in shallow testing or smoke testing. Although it helps check if the API responds, it does not promise thorough testing of specific properties. Response bodies contain information about the output and the success or failure message. That’s why checking for response bodies is essential. For instance, if a DOG API returns a message and status property, check if they exist or if the API consumers expect specific properties in the JSON object; ensure they are present.

There are various ways to check the response bodies built into Supertest. For example, you can pass a string or regular expression to the expect() method. The string should match the whole body, and the regular expression would review parts of it. Now that we know the basics of installing and performing Supertest, let’s find out what developers and testers can test.