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= Tests Style Guide =

This page documents conventions for our Launchpad tests.
Reviewers make sure that code merged is documented and covered by
tests. Following the principles outlined in this document will minimize
comments related to test style from reviewers.

Reviewers will block merge of code that is under-documented or
under-tested. We have two primary means of documentation:

    1. System documentation in `doc` directories such as `lib/lp/<app>/doc`.
    1. Page tests in `lib/lp/<app>/stories`.
    1. View tests in `lib/lp/<app>/browser/tests`.

While these two types of documentation use the doctest format, which means
that they contain testable examples, they are documentation first. So they
are not the best place to test many corner cases or various similar
possibilities. This is best done in other unit tests or functional
tests, which have ensuring complete test coverage as their main objective.

== Testable Documentation ==

Testable documentation includes system documentation doctests and page
tests.

What do we mean by "testable documentation"? One rule of thumb is the narrative should be similar to
what you'd see in an API reference manual. Another trick to ensure the narrative is appropriately detailed
is to mentally remove all of the code snippets and see if the narrative stands by itself.

=== System Documentation ===

These are doctests located under `lib/lp/<app>/doc`. They
are used to document the APIs and other internal objects. The
documentation should explain to a developer how to use these objects
and what purpose they serve.

Each modification to `lp.<app>.interfaces` should be
documented in one of these files.

(Each file in that directory is automatically added to the test suite.
If you need to configure the test layer in which the test will be run or
need to customize the test fixture, you can add special instructions for
the file in the system documentation harness in
`lib/lp/<app>/tests/test_doc.py`.)

=== Use Cases Documentation: Page Tests ===

We use page tests to document all the use cases that Launchpad satisfies.
The narrative in these files should document the use case. That is,
they should explain what the user's objective is and how he accomplishes
it.

The examples in these files uses `zope.testbrowser` to show how the
user would navigate the workflow relevant to the use case.

So each addition to the UI should be covered by an appropriate section
in a page test.

The page tests do not need to document and demonstrate each and every
possible way to navigate the workflow. This can usually be done in a
more direct manner by testing the view object directly.

(See PageTestsOrSystemDocs for background discussion on using a system
doctest vs a page test.)

=== Browser View Tests ===

View objects are usually documented that way along other system objects in files
named `*-pages.txt` or in `lib/lp/<app>/browser/tests/*-views.txt`.

The browser tests directory contains both doctest files for documenting the use of browser view classes
and unit tests (e.g. `test_*.py`) for performing unit tests, including covering corner cases.
Currently some apps, registry for example, have a large number of doctests in this location
that are not strictly testable documentation. Over time these non-documentation doctest files should be
converted to unit tests.

'''All new browser tests that are not testable documentation should be written as unit tests.'''

=== Common Conventions ===

The basic conventions for testable documentation are:

  * Example code is wrapped at 78 columns, follows regular [[https://launchpad.readthedocs.io/en/latest/guides/python.html|Python style guide]], and is indented 4 spaces.
  * Narrative text may be wrapped at either 72 or 78 columns.
  * You can use regular Python comments for explanations related to the code and not to the documentation.
  * Doctests use Restructured Text (or "ReST", see http://docutils.sourceforge.net/docs/user/rst/quickref.html).
   * We use ReST because it's what the Python community have standardized on and because it makes setting up Sphinx to browse all the doctests simpler.
  * The file should have a first-level title element. An expansion of the filename is usually a good start. For example, the file bugcomment.txt could have this title:

  {{{
Bug Comments
============
}}}
  * Two blank lines are used to separate the start of a new section (a header).

  {{{
An Example
---------

Launchpad tracks foo and bar elements using the IFooBarSet utility.

    >>> from lp.foo.interfaces.bar import IBar, IFoo, IFooBarSet
    >>> from lp.testing import verifyObject
    >>> foobarset = getUtility(IFooBarSet)

    >>> verifyObject(IFooBarSet, foobarset)
    True

You use the getFoo() method to obtain an IFoo instance by id:

    >>> foo = foobarset.getFoo('aFoo')
    >>> verifyObject(IFoo, foo)
    True

Similarly, you use the getBar() method to retrieve an IBar instance by
id:

    >>> bar = foobarset.getBar('aBar')
    >>> verifyObject(IBar, bar)
    True
}}}

Each individual test should be of the form:

{{{
     >>> do_something()
     expected output
}}}

This means that something like this isn't considered a test, but test
setup (since it doesn't produce any output)

{{{
    >>> do_something()
}}}

For the reason above, the assert statement shouldn't be used in doctests.


=== Comparing Results ===

When writing doctest, make sure that if the test fails, the failure
message will be helpful to debug the problem. Avoid constructs like:

    {{{
    >>> 'Test' in foo.getText()
    True
}}}

The failure message for this test will be:

    {{{
- True
+ False
}}}

which isn't helpful at all in understanding what went wrong. This
example is a lot more helpful when it fails:

    {{{
    >>> foo.getText()
    '...Test...'
}}}

For page tests, where the page contains a lot of elements, you should
zoom in to the relevant part. You can use the `find_main_content()`,
`find_tags_by_class()`, `find_tag_by_id()`, and `find_portlet()` helper
methods. They return `BeautifulSoup` instances, which makes it easy
to access specific elements in the tree.

    {{{
The new status is displayed in the portlet.

    >>> details_portlet = find_portlet(browser.contents, 'Question details')
    >>> print(details_portlet.find('b', text='Status:').next.strip())
    Needs information
}}}

There is also an `extract_text()` helper that only renders the HTML text:

    {{{
    >>> print(extract_text(
    ... find_tag_by_id(browser.contents, 'branchtable')))
    main 60 New firefox
    klingon 30 Experimental gnome-terminal
    junk.contrib 60 New 2005-10-31 12:03:57 ... weeks ago
}}}

Read PageTests for other tips on writing page tests.


=== When to print and when to return values ===

Doctests mimic the Python interactive interpreter, so generally it's preferred
to simply return values and expect to see their string representation. In a
few cases though, it's better to `print` the results instead of just returning
them.

The two most common cases of this are `None` and strings. The interactive
interpreter suppresses `None` return values, so relying on these means the
doctest makes less sense. You could compare against `None`, but the `True` or
`False` output isn't explicit, so it's almost always better to print values
you expect to be `None`.

Instead of:

{{{
>>> should_be_none()
>>> do_something_else()
}}}

Use:

{{{
>>> print(should_be_none())
None
>>> do_something_else()
}}}

For a different reason, it's also usually better to print string results
rather than just returning them. Returning
the string causes the quotes to be included in the output, while printing the
string does not. Those extra quotes are usually noise.

Instead of:

{{{
>>> get_some_text()
'foo'
>>> get_some_string()
"Don't care"
}}}

Use:

{{{
>>> print(get_some_text())
foo
>>> print(get_some_string())
Don't care
}}}

=== Dictionaries and sets ===

You can't just print the value of a dictionary or a set when that collection
has more than one element in it, e.g.

{{{
>>> print(my_dict)
{'a': 1, 'b': 2}
}}}

The reason is that Python does not guarantee the order of its elements in a
dictionary or set, so the printed representation of a dictionary is
indeterminate. In page tests, there's a `pretty()` global which is basically exposing Python's
pretty printer, and you can use it safely:

{{{
>>> pretty(my_dict)
{'a': 1, 'b': 2}
}}}

Though it's a bit uglier, you can also print the sorted items of a dictionary:

{{{
>>> sorted(my_dict.items())
[('a', 1), ('b', 2)]
}}}

=== Global State ===

Be especially careful of test code that changes global state. For example, we were recently bit by code in a test that did this:

{{{
socket.setdefaulttimeout(1)
}}}

While that may be necessary for the specific test, it's important to understand that this code changes global state and thus can adversely affect all of our other tests. In fact, this code caused intermittent and very difficult-to-debug failures that mucked up PQM for many unrelated branches.

The guideline then is this: ''If code changes global state (for example, by monkey-patching a module's globals) then the test '''must''' be sure to restore the previous state, either in a `try`-`finally` clause, or at the end of the doctest, or in the test's `tearDown` hook.''

=== Style to Avoid ===

A very important consideration is that documentation tests are really
'''documentation''' that happens to be testable. So, the writing style
should be appropriate for documentation. It should be affirmative and
descriptive. There shouldn't be any phrases like:

    * Test that...
    * Check that...
    * Verify that...
    * This test...

While these constructs may help the reader understand what is happening,
they only have indirect value as documentation. They can usually be
replaced by simply stating what the result is.

For example:

    {{{
Test that the bar was added to the foo's related_bars:

    >>> bar in foo.related_bars
    True
}}}

Can be replaced by:

    {{{
After being linked, the bar is available in the foo's
related_bars attribute:

    >>> bar in foo.related_bars
    True
}}}

Also, use of "should" or "will" can usually be replaced by the present tense
to make the style affirmative.

For example:

    {{{
The bar not_a_foo attribute should now be set:

    >>> bar.not_a_foo
    True
}}}

Can be replaced by:

    {{{
The bar not_a_foo attribute is set after this operation:

    >>> bar.not_a_foo
    True
}}}

A good rule of thumb to know whether the narrative style works as
documentation is to read the narrative as if the code examples where not
there. If the text style makes sense, the style is probably good.


=== Using Sample Data ===

If possible, avoid using the existing sample data in tests, apart
from some basic objects, like users. Sample data is good for
demonstrating the UI, but it can make tests harder to understand, since
it requires knowledge of the properties of the used sample data.
Using sample data in tests also makes it harder to modify the data.

If you do use sample data in the test, assert your expectations to avoid
subtle errors if someone modifies it. For example:

{{{
Anonymous users can't see a private bug's description.

    >>> private_bug = getUtility(IBugSet).get(5)
    >>> private_bug.private
    True

    >>> login(ANONYMOUS)
    >>> private_bug.description
    Traceback (most recent call last):
    ...
    Unauthorized:...

}}}

When using fake domains and '''especially''' fake email addresses, wherever
possible use the `example.{com,org,net}` domains, e.g. `aperson@example.com`.
These are guaranteed by Internet standard never to exist, so it can't be
possible to accidentally spam them if something goes wrong on our end.

=== Fixtures and Helpers ===

Sometimes a lot of code is needed to set up a test, or to extract the
relevant information in the examples. It is usually a good idea to
factor this code into functions that can be documented in the
file itself (when the function will only be used in that file), or even
better, moved into a test helper module from which you can import.

These helpers currently live in `lib/lp/testing'.
New helpers should go there, unless they're very specific to a particular corner of the application; in such cases you can use something like `lp.foo.testing`.

== Functional and Unit Tests ==

Complete test coverage without impairing documentation often requires
dedicated functional or unit tests. In Launchpad, Python test cases are
used for these types of tests. You may encounter legacy code that uses
doctests for functional testing. If you do, please consider converting
it to a Python test case.

Functional tests are found in the `tests` subdirectory of each directory
containing code under test.

=== Python Test Cases ===

Although Python test cases are not documentation they must still be
human-readable. So:

    * Keep the test short and concise.
    * Stick to the "setup, exercise, assert" pattern, especially avoid "exercise, assert, exercise some more, assert".
    * Put into the docstring of each test case what is being tested. As a special case for test methods, a comment block at the beginning of the method is considered an acceptable substitute to a docstring. Please observe "Style to avoid", as explained above.
    * Organize related test cases in the same class. Explain test objectives in the class docstring.
    * When asserting for equality use the form `assertEqual(expected_results, actual_results, "...")` (the third argument is optional, for use if failure messages would otherwise be particularly unclear).
    * Make sure that each assert fails with an appropriate error message explaining what is expected. `lp.testing.TestCase` and `TestCaseWithFactory` are derived from `testtools.TestCase` and therefore produce good error messages. Only some cases may warrant an explicit error message.

        For example, this

        {{{
self.assertTrue('aString' in result)
        }}}

        could be replaced by:

        {{{
self.assertIn('aString', result)
        }}}

    * Consider using testtools matchers where reasonable. These can often improve failure messages so that they show more information in one go, which can be useful when debugging mysterious failures.

        For example, instead of this: {{{
self.assertEqual('expected', obj.foo)
self.assertEqual('more expected', obj.bar)
        }}}
        prefer this: {{{
self.assertThat(obj, MatchesStructure.byEquality(
    foo='expected',
    bar='more expected'))
        }}}

In general, you should follow Launchpad coding conventions (see
[[https://launchpad.readthedocs.io/en/latest/guides/python.html|Python style guide]]), however when naming test methods:

 * Use PEP 8 names, e.g. `test_for_my_feature()`
 * When testing a specific Launchpad method, a mix of PEP 8 and camel case is
 used, e.g. `test_fooBarBaz()`
 * When testing alternatives for a LP method, use this style:
 `test_fooBarBaz_with_first_alternative()`,
 `test_fooBarBaz_with_second_alternative()`, etc.


== How To Use the Correct Test URL ==

When tests run, and need to connect to the application server instance under test, you need to ensure that a URL with the correct port for that test instance is used. Here's how to do that.

The config instance has an API which allows the correct URL to be determined. The API is defined on !CanonicalConfig and as a convenience is available as a class method on !BaseLayer.

    {{{

def appserver_root_url(self, facet='mainsite', ensureSlash=False):
    """Return the correct app server root url for the given facet."""
}}}

Code snippets for a number of scenarios as as follows.

'''Doc Tests'''

    {{{
    >>> from lp.testing.layers import BaseLayer
    >>> root_url = BaseLayer.appserver_root_url()
    >>> browser.open(root_url)
}}}

'''Unit Tests'''

    {{{
class TestOpenIDReplayAttack(TestCaseWithFactory):
    layer = AppServerLayer

    def test_replay_attacks_do_not_succeed(self):
        browser = Browser(mech_browser=MyMechanizeBrowser())
        browser.open('%s/+login' % self.layer.appserver_root_url())

}}}
#refresh 0 https://launchpad.readthedocs.io/en/latest/guides/tests.html

TestsStyleGuide (last edited 2021-11-25 16:17:44 by cjwatson)