===================
Zope 3 Unit Testing
===================

How to run Zope 3 unit tests
============================

In the top level directory, run::

    $ python test.py

This runs all unit tests silently (unless errors occur).  It is possible to
run the tests more verbosely or to be more selective about which tests to run.
There are also other options.  For information about all this, run "python
test.py -h" which prints an extensive usage message.

Zope Testing
============

If you encounter a directory named "tests" in a package within within the Zope
source code, it most likely indicates that the directory contains test code
used to ensure that the code owned by the package works as it was designed.


What Unit Tests Are
===================

A "unit" may be defined as a piece of code with a single intended purpose.  A
"unit test" is defined as a piece of code which exists to codify the intended
behavior of a unit and to compare its intended behavior against its actual
behavior.

Unit tests are a way for developers and quality assurance engineers to quickly
ascertain whether independent units of code are working as expected.  Unit
tests are generally written at the same time as the code they are intended to
test.  A unit testing framework allows a collection of unit tests to be run
without human intervention, producing a minimum of output if all the tests in
the collection are successful.

What Unit Tests Are Not
=======================

It's very useful to define unit tests in terms of what they are not.  From the
"Extreme Programming Enthusiast" website
(http://c2.com/cgi/wiki?UnitTestsDefined)::

Unit tests are not:

- Manually operated.

- Automated screen-driver tests that simulate user input (these are
  "functional tests").

- Interactive.  They run "no questions asked."

- Coupled.  They run without dependencies except those native to the thing
  being tested.

- Complicated.  Unit test code is typically straightforward procedural code
  that simulates an event.

Unit Testing Frameworks
=======================

A unit testing framework is generally employed to collect related unit tests
together in order to make it easier to run them as a group.  When used with a
unit testing framework, unit tests live outside of the modules of code they're
intended to test.

How Unit Tests Help In The Development Process
==============================================

Unit tests should be written at the same time the code they test is written.
A short, healthy cycle of "code/write test/run test/repeat" can help a
developer code more quickly by reducing "backtracking" effort and by helping
the developer focus on the actual problem at hand.  Additionally, the unit
tests generated at initial development time can serve as later assurance that
maintenance and refactoring performed on code does not break any of its
intended functionality or behavior.  The results of unit tests may
additionally be used as a metric by quality assurance personnel along with the
results of other tests to gauge code quality before before it is "shipped."

Basic Unit Testing Philosophies
===============================

Write unit tests at the same time that you write the code.  Nothing's worse
than being faced with the prospect of writing tests against a huge chunk of
existing code because you "have to." Writing unit tests post-facto can be
boring and also robs you of the main benefits that unit testing can provide.
Writing unit tests at the same time you write the code helps you focus on the
task at hand.  Writing unit tests in conjunction with code can be fun and
satisfying, and can help you improve the quality of your code while its goals
are fresh in your mind.  Used properly, unit testing may also help you write
code faster, because you will need to "backtrack" less.  Some "Extreme
Programming" enthusiasts posit that you should write a test before you write
its associated code, and then develop the code until it passes the test.

Unit tests should be developed against as small and specific a subset of a
system's or subsystem's functionality as possible.  For instance, a one unit
test may test that a unique id generator produces ids of a specific length,
while another unit test in the same group may ensure that a thousand ids from
the same unique id generator do not contain the same value.  Writing a single
unit test which tests a broad swath of a system's capabilities is
counterproductive, because it does not allow for a fine enough granularity
when attempting to figure out "what went wrong," requiring the developer to
"backtrack".  Unit testing is capable of helping to help reduce backtracking,
but only if used properly.

A unit test does not produce any output unless it fails.  If a unit test
fails, it should print something useful, but short.  A unit test should never
fill the screen with output or otherwise produce output that needs to be
manually examined for "clues".  This is the realm of other testing
methodologies.  If unit tests are written at sufficiently granular level, it
is often enough just to know the name of the unit test that failed.

"It is better to have tried to test and failed than to not have tried to test
at all" aka "test the riskiest things first."  If the prospect of writing a
series of unit tests for an existing system seems daunting, it's important to
remember that no matter how many unit tests you write, you cannot prove that
your software does not have bugs.  Therefore, you cannot possibly test every
case while developing.  You should plan to write tests against code based on
the risks involved in not testing that code.  Don't feel that you need to
write a test case for every "corner case" (although do try to hit the riskiest
ones).  In the worst case, it's better to have a test module with one lonely
unit test in it than none at all.

"Test fixtures" are employed by unit tests.  Test fixtures are bits of state
and environment that allow the unit test to perform its job properly.  An
example of a test fixture might be a file, an instance of a class, or a row in
a database table.  Any part of the environment needed by a unit test besides
the unit testing framework itself is considered a test fixture.

In general, the common fixtures required by individual tests in a testing
group should be more or less identical.  If the fixtures needed by a single
test are radically different than the fixtures required by the rest of the
tests, or if the test does not require the fixtures provided to the other
tests, it probably belongs in another (or its own) group of tests.

When a unit test in a group modifies the state of a test fixture, the test
fixture should be restored to a known state before the next unit test in the
group is run.  Often, this means "rolling back" changes to a transactional
database or restoring the state of a string so the next unit test can inherit
a known state of the same fixtures.  The unit testing framework has
capabilities which allow you to automate most of this work by providing a "set
up" method which gets called before each test is run and a "tear down" method
that gets called after a test is finished.

Unit tests should play nicely with the unit testing framework they employ.
Unit tests should not call "sys.exit()" or do similar things which effect
their ability to be run as part of a group of tests.  The testing framework
attempts to deal with misbehaved unit tests, but it's better just to make them
behave nicely in the first place.

Unit tests should "grow" with the code that they're intended to test.  For
example, if a group of unit tests is intended to verify the behavior of all of
the routines within a module, additional unit tests should be added to the
test group when new functionality is added to that module.

Writing Unit Tests For The Zope Core
====================================

If you're not writing core code, you probably don't need to listen to any more
of this.  :-) The rules for writing tests for Zope core code are simple:

- The testing code should make use of the standard Python unittest module.
  See the Python docs for usage information.

- Tests must be placed in a "tests" subdirectory of the package or directory
  in which the core code you're testing lives.

- Test modules should be named something which represents the functionality
  they test, and should begin with the prefix "test." E.g., a test module for
  BTree should be named testBTree.py.

- An individual test module should take no longer than 60 seconds to complete.

More information is available at::

    http://dev.zope.org/Zope3/WritingUnitTests

Writing Unit Tests For Applications Based On Zope
=================================================

Zope uses the standard Python unittest module.  See the Python docs for usage
information.  You should establish your own conventions for naming and
placement of test modules.

Writing unit tests against applications based on Zope can be difficult.  Zope
is a collection of related modules, some with non-trivial interdependencies.
Running its code successfully also in some cases depends on state provided
only in the context of a web request, so calling Zope methods directly may not
work as you expect.  If you're not intimately familiar with Zope, implementing
unit tests can be frustrating.  For example, for the common case, before you
are able to write code which tests a Zope SQL Method, you must establish a
test fixture which represents your entire Zope site.

Luckily, some tools are at your disposal to make writing unit tests against
Zope components and applications easier by making the creation of these
fixtures easier.

Surprisingly, one of the most effective tools for facilitating unit testing is
ZEO (http://www.zope.org/Products/ZEO).  ZEO is an open-source clustering
solution for Zope which makes it possible to front-end a single "storage
server" which manages a Zope object database with multiple Zope clients that
run a "client storage".  The reason ZEO is interesting for unit testing is
mostly an unintended side-effect of how it works as compared to Zope without
ZEO.  Zope without ZEO commonly uses a "FileStorage" to hold its object
database.  When Zope is started with a FileStorage, the FileStorage code
processes an "index" file.  This takes time.  Zope using a ClientStorage as
with ZEO does not process an index file, making startup faster.  Fast startup
of Zope is critical to effective unit testing.  It is recommended that you
implement ZEO if you're heavy in to unit testing, as it really speeds things
up.  It's not strictly required, however.

Administrivia
=============

Unit test scripts found in the Zope source code are based on the PyUnit unit
testing framework, available from http://pyunit.sourceforge.net, written by
Stephen Purcell (thanks Stephen!).  PyUnit is based on the JUnit testing
framework for Java (written by Kent Beck and Erich Gamma), which in turn was
based on a testing framework designed for Smalltalk (also written by Kent
Beck).

Unit testing is a primary tenet of "Extreme Programming", a software
development methodology designed to facilitate the rapid production of high
quality code with a minimum of developmental ceremony.  For more information
on unit tests as they relate to Extreme Programming, see
http://c2.com/cgi/wiki?UnitTestsDefined.  Although Digital Creations has not
embraced the entire spectrum of Extreme Programming methodologies in its
software development process, we've found unit tests a way to speed
development and produce higher-quality code.
