Testing Typescript Api With Jest and Supertest

We are going to be using the very simple TypeScript API we developed in a previous tutorial in order to learn about Jest Testing.

In this tutorial, we’ll be looking at how you can get a very simple test framework up and running for your TypesScript based API using the jest and supertest testing libraries.

Installation

Now that we have gotten the why? out of the way, let’s see how we can go about implementing our own testing framework:

First and foremost, we’ll have to install the libraries that we wish to use to test our systems.

$ yarn add ts-jest jest supertest

Once you have installed the above packages, you will have to add the test script to your package.json file within your project:

{
  // name, version etc.
  "scripts": {
    // other scripts
    "test": "jest"
  },
  // dependencies etc.
  // our jest test suite configuration
  "jest": {
    "moduleFileExtensions": [
      "ts",
      "tsx",
      "js"
    ],
    "transform": {
      "^.+\\.(ts|tsx)$": "ts-jest"
    },
    "globals": {
      "ts-jest": {
        "tsConfigFile": "tsconfig.json"
      }
    },
    "testMatch": [
      "**/__tests__/*.+(ts|tsx|js)"
    ]
  }
}

You’ll notice we’ve also added in the jest configuration to our package.json in the above code snippet. This dictates where jest will be able to find our tests and in this case we’ve dictated they’ll be within our src/__tests__/ directory.

A Simple Test

Ok, so we’ve got the necessary libraries installed, how do we then go about using these to test our codebase?

Well, let’s start by writing a really simple jest test suite that will test a very simple hello API endpoint.

import app from "../app";
import * as request from "supertest";

describe("GET / - a simple api endpoint", () => {
  it("Hello API Request", async () => {
    const result = await request(app).get("/");
    expect(result.text).toEqual("hello");
    expect(result.statusCode).toEqual(200);
  });
});

In the above test suite we have used the supertest library to make a test request against our API endpoint GET "/". This then awaits the response and tests this response to ensure it’s what we expect.

Running our Tests

Now that we’ve got this test case written, let’s try running our test suite by calling the following:

$ yarn run test

This should then return the following output:

✗ yarn run test
yarn run v1.5.1
(node:10360) [DEP0005] DeprecationWarning: Buffer() is deprecated due to security and usability issues. Please use the Buffer.alloc(), Buffer.allocUnsafe(), or Buffer.from() methods instead.
$ jest
 PASS  src/__tests__/app.test.ts
  ✓ Hello API Request (3ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        2.171s
Ran all test suites.
✨  Done in 3.12s.

Excellent, we now have a running, incredibly simple testing framework that we can start to flesh out and use to test every other endpoint or function within our TypeScript based REST API.

Conclusion

I hope you enjoyed this tutorial! If you found it useful and wish to learn more then please feel free to follow me on Twitter where I actively post new stuff: @Elliot_f.