TDD applied to Django API development

Setup the environment

Repl.it

Just click on the following button and login/signup:

In case of missing pytest command just open a Shell tab and follow the "Local setup" steps.

Local setup

python3 -m venv venv
. venv/bin/activate 
pip install -r requirements.txt

For some macOS if pip install fails run this command and then repeat the setup:

export C_INCLUDE_PATH=/Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.8/Headers

Run tests

pytest

Work files

• carts/tests.py: Tests
• carts/views.py: Implementation
• carts/urls.py: List of API urls

Exercises

Remember:

• Write a test
• Run all tests and see it fail
• Write the minimum code to pass the test
• Run all tests and see it pass
• Refactor the code
• Repeat

Exercise 0.0: Retrieve the products in the cart when is empty

• Write a new test case for the GET /cart/ endpoint
• Expect the response to be a 200 status code
• Expect the response.json() to be

{
  "lines": []
}

• Run the tests and see it fail with AssertionError: assert 404 == 200
• Implement the GET /cart/ endpoint with a hardcoded response
• Add the following code to carts/views.py:

def cart_detail(request):
    return JsonResponse(data={"lines": []})

• Run the tests and see it pass
• Refactor the code
• Run the tests and see it pass
• Repeat

Exercise 0.1: Retrieve the products in the cart when has products

• Write a new test case for the GET /cart/ endpoint
• Add a product to the cart CartLine.objects.create(reference="50776", quantity=5)
• Expect the response to be a 200 status code
• Expect the response.json() to be

{
  "lines": [
    {
      "reference": "50776",
      "quantity": 5
    }
  ]
}

• Run the tests and see it fail with AssertionError: assert {'lines': []} == {'lines': [{'reference': '50776', 'quantity': 5}]}
• Fix the implementation to retrieve the products in the cart
• Run the tests and see it pass
• Refactor the code
• Run the tests and see it pass
• Repeat

Exercise 1: Add products to a cart

• Write a new test case for the POST /cart/products/add/ endpoint
• Use the following data to add a product to the cart

{
  "reference": "33333",
  "quantity": 2
}

• Expect the response to be a 200 status code
• Expect the response.json() to be

{
  "lines": [
    {
      "reference": "33333",
      "quantity": 2
    }
  ]
}

• Run the tests and see it fail
• Write the minimum code to pass the test
• Run the tests and see it pass
• Refactor the code
• Run the tests and see it pass
• Repeat

Exercise 2: Substract products from a cart

• Given a cart with 2 products, one with reference 33333 and quantity 4 and another with reference 11111 and quantity 2.
• When I substract a product with reference 33333 and quantity 2.
• Then the cart should have 2 products, one with reference 33333 and quantity 2 and another with reference 11111 and quantity 2.

• Write a new test case for the POST /cart/products/substract/ endpoint
• Use the following data to substract a product from the cart

{
  "reference": "11111",
  "quantity": 2
}

• Expect the response.json() to be

{
  "lines": [
    {
      "reference": "33333",
      "quantity": 1
    },
    {
      "reference": "11111",
      "quantity": 2
    }
  ]
}

• Run the tests and see it fail
• Write the minimum code to pass the test
• Run the tests and see it pass
• Refactor the code
• Run the tests and see it pass
• Repeat

Exercise 4: Add the total quantity of products in the cart

• Given a cart with 2 products, one with reference 33333 and quantity 4 and another with reference 11111 and quantity 1.
• When I retrieve the cart
• Then the cart should have a total quantity of 5.
• And the response should be

{
  "lines": [
    {
      "reference": "33333",
      "quantity": 4
    },
    {
      "reference": "11111",
      "quantity": 1
    }
  ],
  "total_quantity": 5
}

• Run the tests and see it fail
• Write the minimum code to pass the test
• Run the tests and see it pass
• Refactor the code
• Run the tests and see it pass
• Repeat