Prerequisite:
This tutorial is part of the Flask CKEditor Project Series.
⬅ Previous Part ➡ Next Part
Preliminary
Before I begin, please activate the virtual environment and install the required dependencies.
All files and folders remain the same as in the previous tutorial, except I have created a test.py for the purpose of testing the Flask application. For the current tutorial, test.py is where we are running our testing of an application and an SQLite3 database.
In app.py, let me change the SQLite3 connection from
Preliminary
Before I begin, please activate the virtual environment and install the required dependencies.
python -m venv venv
venv\Scripts\activate
pip install pytest
Therefore, an isolated test will provide cleaner and more modular testing.
Before we dive into details, let us figure out the following:
⚙️ What is Pytest?
Pytest helps to check if code works correctly by running small test functions and verifying expected results.
🚀 Why use Pytest?
-
Simple syntax (
assertstatements) - No boilerplate code needed
- Supports fixtures (like your Flask
client) - Great for testing web apps, APIs, and databases
Step 1: Test the Flask application
The app fixture sets up the Flask app and test client, and I have included the code below:
import pytest
from app import app
# ----------------- Fixture -----------------
@pytest.fixture
def client():
# Enable testing mode, so Flask behaves appropriately for tests
app.config['TESTING'] = True
# Disable CSRF protection for testing purposes
# This allows us to submit forms without a CSRF token
app.config['WTF_CSRF_ENABLED'] = False
# Provide the test client
with app.test_client() as client:
# Provide the client to the test functions
yield client
# ----------------- Test Routes -----------------
def test_index(client):
# Test the home page (GET '/')
response = client.get('/')
# Assert that the response returns HTTP 200 (OK)
assert response.status_code == 200
# ----------------- Test Form Submission -----------------
def test_submit_form(client):
# Test submitting the contact form (POST '/message')
response = client.post('/message', data={
'name': 'Kelvin',
'email': 'test@example.com',
'subscribe': 'y',
'message': 'Hello world'
# Follow the redirect to the thank you page
}, follow_redirects=True)
# Assert that the page loaded successfully
assert response.status_code == 200
# Assert that the response contains the success message
# This ensures that form validation passed and redirect worked
assert b"sent successfully" in response.data.lower()The routes test checks whether the application loads to contact.html; if it does, it passes the first test.
The second test is whether Pytest can imitate the user adding data to the respective fields, such as entering "Kelvin" in the name field. Next, it will be redirected to the thankyou.html, and if it succeeds, then it will pass the test. In the terminal, I run the code below:
pytest flask_ckeditor/test.py
If the above test passes, I can now conduct further tests on the SQLite3 database.
Step 2: Test the SQLite3 database
A database fixture is used to set up a temporary SQLite database and tables in app.py, as shown below.
import sqlite3
conn = sqlite3.connect("flask_ckeditor/message.db")conn = sqlite3.connect(app.config.get('DATABASE', 'flask_ckeditor/message.db'))import pytest
from app import app
import sqlite3
# ----------------- Fixture -----------------
@pytest.fixture
def client(tmp_path):
# Enable testing mode, so Flask behaves appropriately for tests
app.config['TESTING'] = True
# Disable CSRF protection for testing purposes
app.config['WTF_CSRF_ENABLED'] = False
# Use a temporary SQLite database for testing
test_db = tmp_path / "test_message.db"
app.config['DATABASE'] = str(test_db)
# Initialize database table for test
conn = sqlite3.connect(app.config['DATABASE'])
c = conn.cursor()
c.execute("""
CREATE TABLE message (
id INTEGER PRIMARY KEY AUTOINCREMENT,
name TEXT NOT NULL,
email TEXT NOT NULL,
subscribe BOOLEAN,
message TEXT NOT NULL
)
""")
conn.commit()
conn.close()
with app.test_client() as client:
yield client
# ----------------- Test Database Insert -----------------
def test_db_insert(client):
"""
Test that submitting the form actually inserts data into the database
"""
# Submit form data
client.post('/message', data={
'name': 'Kelvin',
'email': 'test@example.com',
'subscribe': 'y',
'message': 'Hello world'
}, follow_redirects=True)
# Connect to the temporary test database
conn = sqlite3.connect(app.config['DATABASE'])
c = conn.cursor()
# Retrieve all rows from the 'message' table
c.execute("SELECT * FROM message")
result = c.fetchall()
conn.close()
# Assert that exactly one row was inserted
assert len(result) == 1
# Assert that the data matches what was submitted
row = result[0]
assert row[1] == 'Kelvin' # name
assert row[2] == 'test@example.com' # email
assert row[3] == 1 # subscribe (True stored as 1)
assert row[4] == 'Hello world' # messageAs in the previous test, I will run the same command line again for the current test; the result is shown in the terminal below.
The terminal showed that all three tests had been passed.
Final wrap-up:
In this tutorial, we explored how to test a Flask application using pytest, focusing on form handling and database interactions. We learned how to simulate GET and POST requests, handle Flask-WTF forms, and address common issues like CSRF protection during testing. By using a separate test database, we ensured our tests remain safe and do not affect real data. With these techniques, you can now confidently build reliable, maintainable Flask applications backed by proper automated testing. 🚀
Published: Mar 2026
Last Updated: Mar 2026
About the Author
Kelvin Loh is a Python developer focused on Flask, desktop applications, and business automation solutions. He shares practical tutorials and real-world coding projects to help developers and small businesses build useful applications.
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