Flask-Testing

The Flask-Testing extension provides unit testing utilities for Flask.

Installing Flask-Testing

Install with pip and easy_install:

pip install Flask-Testing

or download the latest version from version control:

git clone https://github.com/jarus/flask-testing.git
cd flask-testing
python setup.py develop

If you are using virtualenv, it is assumed that you are installing Flask-Testing in the same virtualenv as your Flask application(s).

Writing tests

Simply subclass the TestCase class:

from flask_testing import TestCase

class MyTest(TestCase):

    pass

You must specify the create_app method, which should return a Flask instance:

from flask import Flask
from flask_testing import TestCase

class MyTest(TestCase):

    def create_app(self):

        app = Flask(__name__)
        app.config['TESTING'] = True
        return app

If you don’t define create_app a NotImplementedError will be raised.

Testing with LiveServer

If you want your tests done via Selenium or other headless browser like PhantomJS you can use the LiveServerTestCase:

import urllib2
from flask import Flask
from flask_testing import LiveServerTestCase

class MyTest(LiveServerTestCase):

    def create_app(self):
        app = Flask(__name__)
        app.config['TESTING'] = True
        # Default port is 5000
        app.config['LIVESERVER_PORT'] = 8943
        return app

    def test_server_is_up_and_running(self):
        response = urllib2.urlopen(self.get_server_url())
        self.assertEqual(response.code, 200)

The method get_server_url will return http://localhost:8943 in this case.

Testing JSON responses

If you are testing a view that returns a JSON response, you can test the output using a special json attribute appended to the Response object:

@app.route("/ajax/")
def some_json():
    return jsonify(success=True)

class TestViews(TestCase):
    def test_some_json(self):
        response = self.client.get("/ajax/")
        self.assertEquals(response.json, dict(success=True))

Opt to not render the templates

When testing with mocks the template rendering can be a problem. If you don’t want to render the templates in the tests you can use the render_templates attribute:

class TestNotRenderTemplates(TestCase):

    render_templates = False

    def test_assert_not_process_the_template(self):
        response = self.client.get("/template/")

        assert "" == response.data

The signal will be sent anyway so that you can check if the template was rendered using the assert_template_used method:

class TestNotRenderTemplates(TestCase):

    render_templates = False

    def test_assert_mytemplate_used(self):
        response = self.client.get("/template/")

        self.assert_template_used('mytemplate.html')

When the template rendering is turned off the tests will also run faster and the view logic can be tested in isolation.

Using with Twill

Twill is a simple language for browsing the Web through a command line interface.

Note

Please note that Twill only supports Python 2.x and therefore cannot be used with Python 3 or above.

Flask-Testing comes with a helper class for creating functional tests using Twill:

def test_something_with_twill(self):

    with Twill(self.app, port=3000) as t:
        t.browser.go(t.url("/"))

The older TwillTestCase has been deprecated.

Testing with SQLAlchemy

This covers a couple of points if you are using Flask-Testing with SQLAlchemy. It is assumed that you are using the Flask-SQLAlchemy extension, but if not the examples should not be too difficult to adapt to your own particular setup.

First, ensure you set the database URI to something other than your production database ! Second, it’s usually a good idea to create and drop your tables with each test run, to ensure clean tests:

from flask_testing import TestCase

from myapp import create_app, db

class MyTest(TestCase):

    SQLALCHEMY_DATABASE_URI = "sqlite://"
    TESTING = True

    def create_app(self):

        # pass in test configuration
        return create_app(self)

    def setUp(self):

        db.create_all()

    def tearDown(self):

        db.session.remove()
        db.drop_all()

Notice also that db.session.remove() is called at the end of each test, to ensure the SQLAlchemy session is properly removed and that a new session is started with each test run - this is a common “gotcha”.

Another gotcha is that Flask-SQLAlchemy also removes the session instance at the end of every request (as should any thread safe application using SQLAlchemy with scoped_session). Therefore the session is cleared along with any objects added to it every time you call client.get() or another client method.

For example:

class SomeTest(MyTest):

    def test_something(self):

        user = User()
        db.session.add(user)
        db.session.commit()

        # this works
        assert user in db.session

        response = self.client.get("/")

        # this raises an AssertionError
        assert user in db.session

You now have to re-add the “user” instance back to the session with db.session.add(user), if you are going to make any further database operations on it.

Also notice that for this example the SQLite in-memory database is used : while it is faster for tests, if you have database-specific code (e.g. for MySQL or PostgreSQL) it may not be applicable.

You may also want to add a set of instances for your database inside of a setUp() once your database tables have been created. If you want to work with larger sets of data, look at Fixture which includes support for SQLAlchemy.

Running tests

with unittest

I recommend you to put all your tests into one file so that you can use the unittest.main() function. This function will discover all your test methods in your TestCase classes. Remember, the names of the test methods and classes must start with test (case-insensitive) so that they can be discovered.

An example test file could look like this:

import unittest
import flask_testing

# your test cases

if __name__ == '__main__':
    unittest.main()

Now you can run your tests with python tests.py.

with nose

The nose collector and test runner works also fine with Flask-Testing.

Changes

0.5.0 (12.06.2016)

  • Improvements to LiveServerTestCase
    • The test case will now block until the server is available
    • Fixed an issue where no request context was available
    • Fixed an issue where tests would be run twice when DEBUG was set to True
  • Add missing message arguments for assertRedirects and assertContext
  • Better default failure message for assertRedirects
  • Better default failure message for assertTemplateUsed
  • Fix an issue that caused the render_templates option to not clean up after itself if set to False
  • Update docs to use new Flask extension import specification

0.4.2 (24.07.2014)

  • Improved teardown to be more graceful.
  • Add message argument to assertStatus respectively all assertion methods with fixed status like assert404.

0.4.1 (27.02.2014)

This release is dedicated to every contributer who made this release possible. Thank you very much.

  • Python 3 compatibility (without twill)
  • Add LiveServerTestCase
  • Use unittest2 backports if available in python 2.6
  • Install multiprocessing for python versions earlier than 2.6

0.4 (06.07.2012)

  • Use of the new introduced import way for flask extensions. Use import flask.ext.testing instead of import flaskext.testing.
  • Replace all assert with self.assert* methods for better output with unittest.
  • Improved Python 2.5 support.
  • Use Flask’s preferred JSON module.

API

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