Unit Tests in NodeJS
Tags: node, testing, programming, javascript
Published: 2023-08-14 22:26:26

This will be a series of Unit Tests in X language (or runtime in this case haha). But for now we will stick with the unit tests and then, maybe, we can evolve into integration tests.

I want to start this series as a way of learning tests in some languages and analyze the different aproaches that every language gives to us to start in that important topic. 

The application that we will be testing is a simple ideia that I had with free and open API's. **Unit tests does not involve API's** but I got the idea from one of these API's. 

## And why Unit testing does not involve API's?

I don't know, but I think that some people would disagree with me in this point. But in my opinion, **Unit tests should just test the business rule of your app**. And being an API is just part of your app that you deliver to the client, your application, for example, could answer smoke signals with a sensor, or it could receive messages from a PUB/SUB third party, there are millions of options. If you disagree, PLEASE, chat with me in the comments, I would love to talk to you, and I am not even joking, I really would love to understand why you think that way.

## Continuing

Free API's I said. The idea came from free food API's being more specific [this one](https://www.themealdb.com/api.php). Awesome API here, take a look, maybe you have an idea for a cool project.

Our little project will be a function (that can be atached to anything, from API's to Workers, to recomendation Algorithms), I tried to build it in a very [hexagonal](https://en.wikipedia.org/wiki/Hexagonal_architecture_(software)) way because testing really depends on your architecture, aside from testing you need a good arch that allow you to test without many work arounds (in portuguese we call "gambiarra").

```typescript
export class GetRandomMealUseCase {
  private userFavorites = ["potatoes", "beef"];

  constructor(private mealSerice: IMealService) {}

  async execute(): Promise<
    [Error, { recipe: IMealRecipe; choiceLevel: RandomMealChoice }]
  > {
    try {
      const meal = await this.mealSerice.getRandomMeal();

      const howManyMealTheUserLikes = meal.ingredients.filter(({ name }) =>
        this.userFavorites.includes(name.toLocaleLowerCase())
      ).length;

      const result = { recipe: meal, choiceLevel: RandomMealChoice.Average };

      if (howManyMealTheUserLikes >= 2) {
        result.choiceLevel = RandomMealChoice.ReallyGood;
      } else if (howManyMealTheUserLikes == 1) {
        result.choiceLevel = RandomMealChoice.Good;
      }

      return [null, result];
    } catch (error) {
      return [error as Error, null];
    }
  }
}
```

Basically this is our whole little project. We have a service which just make a HTTP request and some basic error handling, I have choose as a error treatment something like Either where in the first position of the tuple is the error and in the second the response. I added the variable `userFavorites` fixed in the code, but this could be a parameter for our `execute` method.

We have 4 tests that I see for this little file. 1 for each `choiceLevel` and 1 for the error. Let's see how we can make those tests.

**Mocha** and **SinonJS**. We will be using those two fantastic libs for our tests with NodeJS. Mocha for the test cases and SinonJS for our mockings.

## Unit tests

I started creating a mock service so that I could inject it in the use case.

```typescript
export const getRandomMealBaseReturn: IMealRecipe = {
  name: "Mock",
  ingredients: [{ name: "Mock", measure: "1" }],
  instructions: 'Mock'
}

export class MealServiceMock implements IMealService {
  async getRandomMeal(): Promise<IMealRecipe> {
    return getRandomMealBaseReturn;
  }
}
```

That is our mock of MealService. This is guy has a default return that we will mock in other tests so that it satisfies our asserts.

Our first test we just need this base implementation of the meal service to create it so look at it below

```typescript
describe("GetRandomMeal service tests", () => {
  it("Should return a random meal sucessfuly with average meal choice", async () => {
    const useCase = new GetRandomMealUseCase(new MealServiceMock());

    const result = await useCase.execute();

    assert.strictEqual(result[0], null);
    assert.strictEqual(result[1].choiceLevel, RandomMealChoice.Average);
  });
}
```
This first test has just the ideia of returning a meal with average choice and no errors, our next 3 tests will be just mocking the response so that we can test the other branches of the `GetRandomMealUseCase` and the error handling.

And that is it! Check the project over [here](https://github.com/jhonpedro/unit-tests-in-different-langs/tree/main/nodejs). Like I said this will be a series of articles with this same project so, keep an eye here and study tests in other langs with me :)

Thank you!