Example of Effective Mutation Testing Implementation in Spring Boot 3 Projects

The goal of this kata is to demonstrate that 100% code coverage is not a sufficient measure to guarantee that we have a safety net that will notify us if we break something.

How to achieve the goal?

Run the mutation tests only with the unit tests (without the integration and contract tests) and verify that all the mutants are killed.

mvn clean test pitest:mutationCoverage

Acceptance criteria

1. We have an eCommerce Rest API with the following endpoints:

• GET /products

• GET /products/{productId}

• GET /users/{userId}/basket

• POST /users/{userId}/basket

2. When we enter the products page, the list of all products is returned to us:

• GET /products

[
  {
    "id": 1,
    "name": "Dell Latitude 3301 Intel Core i7-8565U/8GB/512GB SSD/13.3",
    "price": "999,00 €"
  },
  {
    "id": 2,
    "name": "Samsonite Airglow Laptop Sleeve 13.3",
    "price": "41,34 €"
  },
  {
    "id": 3,
    "name": "Logitech Wireless Mouse M185",
    "price": "10,78 €"
  },
  {
    "id": 4,
    "name": "Fellowes Mouse Pad Black",
    "price": "1,34 €"
  }
]

3. When we obtain a product by its ID, the related products are returned next to it:

• GET /products/{productId}

{
  "product": {
    "id": 1,
    "name": "Dell Latitude 3301 Intel Core i7-8565U/8GB/512GB SSD/13.3",
    "price": "999,00 €"
  },
  "cross_selling": [
    {
      "id": 2,
      "name": "Samsonite Airglow Laptop Sleeve 13.3",
      "price": "41,34 €"
    },
    {
      "id": 3,
      "name": "Logitech Wireless Mouse M185",
      "price": "10,78 €"
    }
  ]
}

4. We can get a user's basket by their ID.

• GET /users/{userId}/basket

{
  "id": 1,
  "userId": 1,
  "items": {
    "products": [
      {
        "id": 3,
        "name": "Logitech Wireless Mouse M185",
        "price": "10,78 €"
      }
    ]
  }
}

5. If the customer does not have a basket with products, is returned HttpStatus.NOT_FOUND.

6. We can add products to this basket with POST and the payload:

• POST /users/{userId}/basket

{
  "id": 3,
  "name": "Logitech Wireless Mouse M185",
  "price": "10,78 €"
}

8. When we add a product to a basket and the basket does not exist, it is created automatically and the product is added successfully.

9. When we add a product, it already exists in the basket, it is not added.

10. Use PostgreSQL to save the data.

11. Use native queries to manage cross-sell data.

12. This is the example of the table creations.