Functional and system tests with zope.testbrowser


Whilst unit tests and doctests verify the correctness of individual methods and modules, functional tests test portions of the application as a whole, often from the point of view of the user, and typically aligned with use cases. System tests, in comparison, test the entire application as a black box.

No developer likes to click around the browser to check if that button that was only supposed to show up in some cases really did show up. Unfortunately, these are also the types of problems that most often suffer from regressions, because templates are difficult (and slow) to test.

Zope 3 has an elegant library called zope.testbrowser which lets you write doctests that behave like a real web browser (almost… it cannot yet handle JavaScript, which means that testing dynamic UIs that depend on JavaScript is not possible, although Selenium may be a viable alternative here). You can open URLs, click links, fill in form fields and test the HTTP headers, URLs and page contents that are returned from Plone. In fact, you could test any website, not just Zope or Plone ones.

Functional tests are no replacement for unit tests. They test a slice of functionality, typically as the user sees it. Thus, they may not systematically include every aspect of the application. For example, a functional test may check whether a “Delete” button is present, and even that it works as expected, but should not be used to exhaustively test whether the delete operation works in every possible edge case. Where they excel, however, is in testing things like which options appear to which users depending on roles and permissions, or simply to exercise all the various templates used in a given product to make sure they don’t break.

Here is an example from the example.tests package. The test setup is in tests/

"""This is a a functional doctest test. It uses PloneTestCase and doctest
syntax. In the test itself, we use zope.testbrowser to test end-to-end
functionality, including the UI.

One important thing to note: zope.testbrowser is not JavaScript aware! For
that, you need a real browser. Look at zope.testbrowser.real and Selenium
if you require "real" browser testing.

import unittest
import doctest

from Testing import ZopeTestCase as ztc

from example.tests.tests import base

def test_suite():
    """This sets up a test suite that actually runs the tests in the class
    return unittest.TestSuite([

        # Here, we create a test suite passing the name of a file relative
        # to the package home, the name of the package, and the test base
        # class to use. Here, the base class is a full PloneTestCase, which
        # means that we get a full Plone site set up.

        # The actual test is in functional.txt

            'tests/functional.txt', package='example.tests',
            optionflags=doctest.REPORT_ONLY_FIRST_FAILURE |
                        doctest.NORMALIZE_WHITESPACE | doctest.ELLIPSIS),

        # We could add more doctest files here as well, by copying the file
        # block above.


This code is actually identical to the test setup for the integration doctest in the previous section. The differences are found in the actual test itself, which uses Products.Five.testbrowser.Browser, a Zope 2 compatibility wrapper around zope.testbrowser.Browser:

A functional doctest

This is a full-blown functional test. The emphasis here is on testing what
the user may input and see, and the system is largely tested as a black box.
We use PloneTestCase to set up this test as well, so we have a full Plone site
to play with. We *can* inspect the state of the portal, e.g. using
self.portal and self.folder, but it is often frowned upon since you are not
treating the system as a black box. Also, if you, for example, log in or set
roles using calls like self.setRoles(), these are not reflected in the test
browser, which runs as a separate session.

Being a doctest, we can tell a story here.

First, we must perform some setup. We use the testbrowser that is shipped
with Five, as this provides proper Zope 2 integration. Most of the
documentation, though, is in the underlying zope.testbrower package.

    >>> from Products.Five.testbrowser import Browser
    >>> browser = Browser()
    >>> portal_url = self.portal.absolute_url()

The following is useful when writing and debugging testbrowser tests. It lets
us see all error messages in the error_log.

    >>> self.portal.error_log._ignored_exceptions = ()

With that in place, we can go to the portal front page and log in. We will
do this using the default user from PloneTestCase:

    >>> from Products.PloneTestCase.setup import portal_owner, default_password


We have the login portlet, so let's use that.

    >>> browser.getControl(name='__ac_name').value = portal_owner
    >>> browser.getControl(name='__ac_password').value = default_password
    >>> browser.getControl(name='submit').click()

Here, we set the value of the fields on the login form and then simulate a
submit click.

We then test that we are still on the portal front page:

    >>> browser.url == portal_url

And we ensure that we get the friendly logged-in message:

    >>> "You are now logged in" in browser.contents

To learn more, look at the zope.testbrowser documentation and interfaces.
There are also a few examples of testbrowser tests in Plone itself.

All the action happens with the browser object. This simulates a web browser (though as stated above, one that does not support JavaScript), and has a pleasant API for finding form controls and links and clicking on them. The variables browser.url and browser.contents represent what would've been in the URL bar and the rendered view of the page, respectively, and can be examined like any other variable.

zope.testbrowser has pretty comprehensive documentation in its README.txt file - which is, of course, a runnable doctest. In brief, the most important methods of the IBrowser interface (and thus the Browser class) are:

Open a given URL.
Reload the current page, much as the Refresh button in your browser would do.
Simulate pressing the Back button count times.
getLink(text=None, url=None, id=None)
Get an ILink (which you can then call click() on), either by the text inside the <a> tags, by the URL in the href attribute, or the id of the link.
getControl(label=None, name=None, index=None)
Get an IControl, representing a form control, by label (either the value of a submit button or the contents of an associated <label> tag) or form name. The index argument is used to disambiguate if there is more than one control (e.g. index=0 gets the first one). Again, you can call click() on the control object to simulate clicking on it.

The IBrowser interface also provides some properties that can be used to examine the state of the current page. The most important ones are:

The full URL to the current page.
The full contents of the current page, as a string (usually containing HTML tags)
A dict of HTTP headers

Please refer to the interfaces and the README file for details on the other methods and attributes, the interfaces for various types of links and controls, and further examples.

Debugging functional tests

Sometimes you will get errors from Zope resulting from some command executed using the testbrowser. In this case, it can sometimes be difficult to know what the underlying cause is. Two debugging aids exist to make this a bit easier.

First of all, make sure you see all errors in full by setting:

>>> browser.handleErrors = False

If handleErrors is True (the default) you will get errors like HTTPError: HTTP Error 404: Not Found or HTTPError: HTTP Error 500: Internal Server Error. Those are probably not very useful to you. Setting handleErrors to False will show the full exceptions Zope (or possibly the HTML rendering of the error page, depending on the type of error).

Secondly, if you are using PloneTestCase, you can use Plone's error log. At the top of the example, we do:

>>> self.portal.error_log._ignored_exceptions = ()

This means that errors such as NotFound and Unauthorized will be shown in the error log. It may also be useful to enable Verbose Security in zope.conf (see the comments in that file for details). Now, when a line appears that is throwing an error you can't debug, you can do:

>>> try:
...     browser.getControl('Save').click()
... except:
...     print self.portal.error_log.getLogEntries()[0]['tb_text']
...     import pdb; pdb.set_trace()
>>> # continue as normal

This will print the most recent entry in the error log, and set a PDB break point.

Using a real browser to render the results of your tests

Sometimes you would like to see the output of browser.contents in a browser to easily debug what's happening in your functional tests. To do so, place a PDB break point in your tests as described above (import pdb; pdb.set_trace()) and type the following when you get to the PDB prompt while running the tests:

>>> from Testing.ZopeTestCase.utils import startZServer
>>> startZServer()

This will print a tuple like

('', 55143)

containing an IP address and port where you can access the same test site that the testbrowser is working with, in a real browser.

Functional tests vs. system tests

A system test is one which treats the entire system as a black box, interacting with it as a user would. A functional test is more focused on a single "vertical" of functionality, typically linked to a particular use case.

For a functional test, it may be acceptable to examine the internal state of the portal (using self.portal and the PloneTestCase.FunctionalTestCase class to build a test suite) to provide assertions. A system test, by contrast, makes no such assumptions. Ideally, you should be able to point a zope.testbrowser test at a remote site running a fresh installation of your system, and have the tests pass.

Beyond that, the tools used to write a system test are the same. It is only the approach to testing that changes. Whether you need one, or the other, or both, will depend on the level of rigour you need in your tests, and how your system is constructed. In general, though, true system tests are more rare than functional (integration) tests and unit tests.