Writing tests

Testing patterns

Here is explained some of the test basics.

Basic integration testing pattern

  • py.test is launched with test.ini which contains settings your Websauna application uses during the testing, e.g. the name of SQL database where tests write and read data.

  • You have your tests as myapp/tests/test_xxx.py files. How you split test functions to individual files is up to you.

  • test function comes with the test fixtures arguments needed to run the test. Usually they are

    • dbsession clean PostgreSQL where all of your model tables are automatically created. See websauna.tests.conftest.dbsession().
    • web server - a string pointing to http://localhost:8543 or any other address where a web server is running WSGI application with settings from test.ini. See websauna.tests.conftest.web_server().
    • browser - a Splinter browser instance. It’s Firefox by default. You can change it to Chrome with py.test --splinter-webdriver=chrome argument. See pytest_splinter.plugin.browser().
    • init expose websauna.system.Initializer instance of your Websauna application for testing. This is usually required for tests to access init.registry or init.config. See websauna.tests.conftest.init().
  • When test is reading or writing a database with must happen inside a transaction.manager context manager.

  • You can use assert statement to check that the database values are what you expect or that page elements what you expect are present. Using plain assert statement is a py.test speciality. py.test will convert assert statement to something else which gives you a diff output of diverting results.

  • You need to know CSS basics (ids and classes) to be able to identify the elements on the page being tested.

Example test which comes with the default Scaffolds (myapp/tests/test_login.py):

"""An example login test case."""

import transaction
from pyramid.registry import Registry
from sqlalchemy.orm.session import Session
from splinter.driver import DriverAPI

from websauna.tests.utils import create_user
from websauna.tests.utils import EMAIL  # this is [email protected]
from websauna.tests.utils import PASSWORD  # this is random letters
from websauna.system import Initializer

def test_login(web_server: str, browser: DriverAPI, dbsession: Session, registry: Registry):
    """Login as a user to the site.

    This is a functional test. Prepare the test by creating one user in the database. Then try to login as this user by using Splinter test browser.

    :param web_server: Functional web server py.test fixture - this string points to a started web server with test.ini configuration.

    :param browser: A Splinter web browser used to execute the tests. By default ``splinter.driver.webdriver.firefox.WebDriver``, but can be altered with py.test command line options for pytest-splinter.

    :param dbsession: Active SQLAlchemy database session for the test run.

    :param registry: Pyramid registry with all configuration settings from test.ini used to ramp up the test web server

    with transaction.manager:
        # Create a dummy [email protected] user we test
        create_user(dbsession, registry, email=EMAIL, password=PASSWORD)

    # Direct Splinter browser to the website
    b = browser

    # This link should be in the top navigation

    # Link gives us the login form
    assert b.is_element_present_by_css("#login-form")

    b.fill("username", EMAIL)
    b.fill("password", PASSWORD)

    # After login we see a profile link to our profile
    assert b.is_element_present_by_css("#nav-logout")

How tests know about fixtures?

Fixures are just Python function argument names, so how the pytest gets to know where the fixtures are coming from?

When a test run starts, pytest scans both pytest plugins and test folders under a test. If any test folders contains a file named conftest.py pytest imports it. This file has functions with @pytest.fixture decorator to mark possible fixture test functions can use.

The default conftest.py is placed in your project by a Websauna application scaffold. See websauna.tests.conftest for examples.

Useful Splinter functions

You’ll find following Splinter driver API functions useful when writing tests. See Splinter documentation for full information.

Inspecting page elements during test

How do you get known to all CSS element ids, form input names and other page elements you are using in the test?

  • Put a Python pdb breakpoint in a line where you want to write an assert
  • Run test
  • Test execution stops at the breakpoint
  • Use Firefox (or Chrome) Web developer tools and Inspector tool to browse the page.

Here is a test from above with a PDB breakpoint where we want to identify how to check if a login form is present on the page:

def test_login(web_server: str, browser: DriverAPI, dbsession: Session, registry: Registry):

    with transaction.manager:
        # Create a dummy [email protected] user we test
        create_user(dbsession, registry)

    # Direct Splinter browser to the website
    b = browser

    # This link should be in the top navigation

    # Link gives us the login form
    import pdb ; pdb.set_trace()
    assert b.is_element_visible_by_css("???")

Now when you run the test the execution stops on debugger line:

==== test session starts ====
platform darwin -- Python 3.4.2, pytest-2.8.7, py-1.4.31, pluggy-0.3.1
rootdir: /Users/mikko/code/trees/myapp, inifile:
plugins: splinter-1.6.7, flaky-3.0.3, cov-1.8.1, timeout-0.4
collected 1 items

>>>>>>>>>> PDB set_trace (IO-capturing turned off) >>>>>>>>>>>>>
[44] > /Users/mikko/code/trees/myapp/myapp/tests/test_login.py(42)test_login()
-> assert b.is_element_visible_by_css("#login-form")

The test browser (Firefox) should have opened when the test run starts. Now switch to Firefox and you should see the page being tested.


Choose Tools -> Web Developer -> Inspector (This is also available from Firefox right click menu):


Now you can use Inspect tool to examine the page DOM tree and find the id of <form> element:


Pick the id from the inspector and use it with splinter.driver.DriverAPI.is_element_present_by_css().

Functional testing and SQLAlchemy detached object state

When working with functional tests, one has to do real commits for data changes, as otherwise the data cannot be exported across the threads: the thread running unit test functions and another thread being the web server and serving HTTP responses.

This may be pain, as soon as you commit you cannot access SQLAlchemy object attributes anymore, making writing the test code requiring extra boilerplate and loads to avoid all sqlalchemy.orm.exc.DetachedInstanceError exceptions.

This can be avoided by telling SQLAlchemy explicitly to not to detach objects after commit, allowing you to read objects fine in the test methods.

Example conftest.py:

import pytest

def functional_dbsession(request, dbsession):
    """Use this as the last fixture for the functional test functions.

    Commits everything set up in prior fixtures so that they are available cross threads to the web server.
    dbsession.expire_on_commit = False

def box(request, dbsession):
    b = Box.create(dbsession, box_type=BoxType.testing, serial_number=1)
    return b

Example test_api.py:

import binascii
import requests

def test_provision_card(web_server, box, card, functional_dbsession):

    # functional_dbsession as the last argument causes a database commit,
    # but we can still access the model attributes of box and card fine

    data = {
        "box_serial_number": box.hash_id,
        "card_serial_number": binascii.hexlify(card.serial_number),

    response = requests.post(f"{web_server}/api/provision", params=data)

    assert response.status_code == 200, "Got: {}".format(response.text)

    response = response.json()
    assert response["status"] == "ok"
    assert response["ownership_info"]["owner_name"] == "Mikko Ohtamaa"
    assert response["ownership_info"]["owner_phone_number"] == "+18082303437"