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Test-Driven Development#

Test-Driven Development (TDD) is a software development methodology that emphasizes writing tests before implementing the corresponding functionality. This approach ensures that new changes do not unintentionally break existing features and that all functions perform as expected.

Code Coverage#

Code coverage is a metric used in software testing that helps determine the percentage of code that is exercised by tests. It is an essential tool for assessing the effectiveness of your test suite. High code coverage generally indicates that most of your code has been tested, while lower coverage can suggest that some parts of the application may be under-tested, potentially leading to hidden bugs or vulnerabilities.

Codecov.io is a popular tool for tracking and visualizing code coverage. It integrates with various CI/CD pipelines and allows developers to upload their coverage reports.
Once integrated, Codecov provides detailed insights into code coverage trends, coverage gaps, and areas that require further testing.

To integrate Codecov with your project, follow these steps:

  1. Install pytest
    💻 pip install pytest pytest-cov

  2. Add GitHub Action
    📝 .github/workflows/codecov.yml

  3. Create an account
    Create a Codecov account at Codecov.io and link your repository.

  4. Upload the Coverage Report
    After running your tests with coverage, upload the results to Codecov.
    This is done automatically through the CI configuration.

  5. View Coverage Reports
    Once your coverage report is uploaded, you can view detailed insights and trends on the Codecov dashboard.

  6. Code Coverage Badge
    A coverage badge provides a visual indication of the test coverage for the 📝 README.rst page. It is updated automatically as new reports are uploaded to Codecov.

While code coverage is a valuable metric for identifying untested code, high coverage does not necessarily indicate high-quality tests. It only measures the quantity of code exercised during testing, not the quality or effectiveness of those tests. Tests can pass without actually verifying correct behavior, and some areas of the code may be covered by trivial tests that do not expose potential issues. Relying solely on coverage can lead to a false sense of security and might divert attention from other important aspects of testing, such as edge cases and integration scenarios.

Example: Implementing Test Cases for a Django App#

This example demonstrates the TDD approach within a Django app.
You can run all tests in Django using the following command:

💻 `python manage.py test`

To run specific test cases, you can provide the app name and the test case:

💻 `python manage.py test app.MyModelViewTestCase`

This is a Step-by-Step Guide to TDD in Django:

1. Set Up the Django App#

Ensure that you have a Django app in place that you wish to test.

2. Write a Test for the New Feature#

Begin by writing a test for the functionality you intend to implement. For example, if you need to create a view that returns a list of objects from the database, and a corresponding model to represent the database table, your test might look like this:
📝 app/test/my_test.py:

from django.test import TestCase
from myapp.models import MyModel

class MyModelViewTestCase(TestCase):
    def test_list_view_displays_all_objects(self):
        MyModel.objects.create(name="object1")
        MyModel.objects.create(name="object2")
        response = self.client.get('/my-models/')
        self.assertEqual(response.status_code, 200)
        self.assertContains(response, "object1")
        self.assertContains(response, "object2")

3. Run the Test#

At this point, run the test to confirm it fails, as the view has not been implemented yet.
💻 python manage.py test

4. Implement the Model and View#

Implement the model and view to make the test pass.

📝 models.py:

from django.db import models

class MyModel(models.Model):
    name = models.CharField(max_length=255)
    created_at = models.DateTimeField(auto_now_add=True)

    def __str__(self):
        return self.name

📝 views.py:

from django.views.generic import ListView
from myapp.models import MyModel

class MyModelListView(ListView):
    model = MyModel
    template_name = "myapp/my_model_list.html"

5. Run the Test Again#

Run the tests again to ensure the changes pass the test.
💻 python manage.py test

6. Add Additional Tests#

Write additional tests to verify that the view works as expected.
For example, you can test for empty responses:

class MyModelViewTestCase(TestCase):
    def test_list_view_displays_all_objects(self):
        MyModel.objects.create(name="object1")
        MyModel.objects.create(name="object2")
        response = self.client.get('/my-models/')
        self.assertEqual(response.status_code, 200)
        self.assertContains(response, "object1")
        self.assertContains(response, "object2")

    def test_list_view_displays_empty_message(self):
        response = self.client.get('/my-models/')
        self.assertEqual(response.status_code, 200)
        self.assertContains(response, "No objects found.")

7. Run All Tests#

Finally, run all the tests to ensure they pass successfully:
💻 python manage.py test

Conclusion#

TDD provides a structured approach to writing reliable, maintainable software. By ensuring that tests are written before implementing functionality, developers can be confident that new changes will not introduce unintended side effects and that the codebase remains functional and robust over time.

Used Icons

🐙 GitHub | 💠 git | 📝 File | 💻 Command Line