API Design with Node.js V4

Unit test

A unit test is all about testing individual pieces of logic independently of each other. You have to make sure you write your code in a way that can be unit tested.

// not testable
const value = 100;
const action = () => {
  console.log(value);
};
``;

// testable
export const action = (value) => {
  console.log(value);
};

Using arguments vs creating closures and exporting your code are all great patterns to use when creating testable code. Now what does a unit test look like?

describe("user handler", () => {
  it("should do a thing", async () => {
    // .,...

    expect("something").toBe("something");
  });
});

This is how you might write a unit test in Jest. Each it block is an actual test where you usually call some function you want to test, and then create some assertion about what its return value should be. The describe function is just for organizing your test.

Integraion test

Integration tests will test how an entire route works by actually making a request to observe what the API sent back and making assertions on that result. We can use jest along with supertest to run integration test.

import app from "../server";
import request from "supertest";

describe("POST /user", function () {
  it("responds with json", async () {
    const res = await request(app)
      .post("/user")
      .send({ username: "hello", password: "hola" })
      .set("Accept", "application/json")

    expect(res.headers["Content-Type"]).toMatch(/json/);
    expect(res.status).toEqual(200);
  });
});

In this test, we're using the request from supertest to make a request to POST /user, which in our app creates a user. We're sending up the required payload and expect to get a successful 200 when its done.

Now, go write some tests!