Testing file uploads in Flask

Question

I\'m using Flask-Testing for my Flask integration tests. I\'ve got a form that has a file upload for a logo that I\'m trying to write tests for but I keep getting an error sayin

Answer 1

While trying to find a bug in my code I've created a SSCCE for file upload (based on the docs) with a corresponding test based on other answers here. It might be useful for somebody:

app.py:

import base64
import os
import pathlib
import tempfile
import textwrap

import flask
import werkzeug.utils

root = flask.Blueprint('root', __name__)

@root.route('/', methods=['GET', 'POST'])
def upload_file():
    if flask.request.method == 'POST':
        try:
            file = flask.request.files['file']
            if not file.filename:
                raise LookupError()
            filename = werkzeug.utils.secure_filename(file.filename)
            file.save(pathlib.Path(flask.current_app.config['UPLOAD_FOLDER'], filename))
            flask.flash('File saved!', 'message')
        except LookupError:
            flask.flash('No file provided!', 'error')
        return flask.redirect(flask.url_for('root.upload_file'))
    else:
        return flask.render_template_string(textwrap.dedent(
            '''\
            
            
            {% with messages = get_flashed_messages(with_categories=true) %}{% if messages %}
            

            {% for category, message in messages %}
{{ message }}
            {% endfor %}
            
            {% endif %}{% endwith %}
            
Upload new File
            

            
            
            
            '''
        ))

def create_app():
    app = flask.Flask(__name__)
    app.config['UPLOAD_FOLDER'] = tempfile.gettempdir()
    app.secret_key = 'change-me'
    app.register_blueprint(root)
    return app

if __name__ == '__main__':
    create_app()

test_app.py:

"""upload tests"""

import base64
import io
import unittest

import werkzeug

import app

# https://raw.githubusercontent.com/mathiasbynens/small/master/jpeg.jpg
SMALLEST_JPEG_B64 = """\
/9j/2wBDAAMCAgICAgMCAgIDAwMDBAYEBAQEBAgGBgUGCQgKCgkICQkKDA8MCgsOCwkJDRENDg8Q
EBEQCgwSExIQEw8QEBD/yQALCAABAAEBAREA/8wABgAQEAX/2gAIAQEAAD8A0s8g/9k=
"""

class BaseTestCase(unittest.TestCase):
    def test_save(self):
        with app.create_app().test_client() as client:
            file = werkzeug.datastructures.FileStorage(
                stream=io.BytesIO(base64.b64decode(SMALLEST_JPEG_B64)),
                filename="example image.jpg",
                content_type="image/jpg",
            )
            response = client.post(
                '/',
                data=dict(
                    file=file,
                ),
                follow_redirects=True,
                content_type='multipart/form-data',
            )