Tutorial: Python Django App

This tutorial walks through adding nolapse coverage enforcement to a Django application. It covers pytest-cov configuration, baseline creation, regression simulation, and CI integration.

Time to complete: 20–30 minutes.

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Prerequisites

• Python 3.9 or later
• nolapse CLI installed (go install github.com/nolapse/nolapse-cli/nolapse-cli/cmd/nolapse@latest)

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Part 1 — Create the Django App

1.1 Set up the project

mkdir hello-django && cd hello-django
git init
python3 -m venv .venv
source .venv/bin/activate
pip install django pytest pytest-cov pytest-django
django-admin startproject config .
python manage.py startapp greet

1.2 Write a view

Edit greet/views.py:

from django.http import JsonResponse


def health(request):
    return JsonResponse({"status": "ok"})


def greet(request):
    name = request.GET.get("name", "world")
    return JsonResponse({"message": f"Hello, {name}!"})

Edit config/urls.py:

from django.urls import path
from greet import views

urlpatterns = [
    path("health/", views.health),
    path("greet/", views.greet),
]

1.3 Configure pytest

Create pytest.ini:

[pytest]
DJANGO_SETTINGS_MODULE = config.settings
addopts = --cov=greet --cov-report=json --cov-report=term-missing

1.4 Write the tests

Create greet/tests.py:

import pytest
from django.test import Client


@pytest.fixture
def client():
    return Client()


def test_health(client):
    response = client.get("/health/")
    assert response.status_code == 200
    assert response.json() == {"status": "ok"}


def test_greet_default(client):
    response = client.get("/greet/")
    assert response.status_code == 200
    assert response.json() == {"message": "Hello, world!"}


def test_greet_named(client):
    response = client.get("/greet/?name=Alice")
    assert response.status_code == 200
    assert response.json() == {"message": "Hello, Alice!"}

1.5 Run the tests

pytest

Expected output (last lines):

---------- coverage: platform linux, python 3.12 ----------
Name              Stmts   Miss  Cover
-------------------------------------
greet/views.py        8      0   100%
-------------------------------------
TOTAL                 8      0   100%

3 passed in 0.42s

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Part 2 — Add nolapse

2.1 Initialise the baseline

nolapse init --repo . --lang python

Expected output:

measuring coverage...
coverage: 100.00%
baseline written to .audit/coverage/baseline.md
nolapse.yaml created

2.2 Inspect the files

cat .audit/coverage/baseline.md

coverage: 100.00%
timestamp: 2026-03-18T09:00:00Z
commit: a1b2c3d4e5f6a1b2c3d4e5f6a1b2c3d4e5f6a1b2

cat nolapse.yaml

lang: python
warn_threshold: 0.5
fail_threshold: 1.0

2.3 Commit the baseline

git add .audit/coverage/baseline.md nolapse.yaml greet/ config/ pytest.ini manage.py
git commit -m "chore: add nolapse coverage baseline"

2.4 Run a coverage check

nolapse run --repo . --lang python

Expected output:

file  baseline coverage  PR coverage  delta    outcome
.     100.00%            100.00%      +0.00%   pass

outcome: pass  delta: +0.00  coverage: 100.00%  baseline: 100.00%

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Part 3 — Simulate a Regression

3.1 Remove a test

Delete test_greet_named from greet/tests.py. Save the file.

3.2 Run nolapse

nolapse run --repo . --lang python

Expected output:

file  baseline coverage  PR coverage  delta    outcome
.     100.00%            87.50%       -12.50%  fail

outcome: fail  delta: -12.50  coverage: 87.50%  baseline: 100.00%
warn_threshold: 0.5  fail_threshold: 1.0

Exit code is 1. The regression was detected.

3.3 Restore the test

Add test_greet_named back. Re-run:

nolapse run --repo . --lang python

file  baseline coverage  PR coverage  delta    outcome
.     100.00%            100.00%      +0.00%   pass

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Part 4 — Add the GitHub Action

Create .github/workflows/coverage.yml:

name: Coverage check

on:
  pull_request:

jobs:
  coverage:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - name: Set up Python
        uses: actions/setup-python@v5
        with:
          python-version: "3.12"

      - name: Install dependencies
        run: pip install django pytest pytest-cov pytest-django

      - name: Run nolapse
        uses: nolapse/nolapse-action@v1
        with:
          repo-token: ${{ secrets.GITHUB_TOKEN }}
          lang: python
          warn-threshold: "0.5"
          fail-threshold: "1.0"

Commit and push:

git add .github/workflows/coverage.yml
git commit -m "ci: add nolapse coverage gate"
git push -u origin main

Open a pull request. The coverage check runs automatically on every PR.

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What You Built

• A Django app with views tested via pytest-django
• pytest.ini configured to generate coverage.json on every run
• A nolapse baseline committed to git
• A GitHub Actions workflow enforcing coverage on every PR

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Next Steps

• Exclude Generated Code — exclude Django migrations from coverage
• Raise Your Coverage Threshold — tighten enforcement over time
• Multi-Language Projects — add a Go service alongside the Django app