Fleshed out the tests documentation

The doctest bit still needs some work, I've never really used it myself
so not sure what the benefits are :)

docs/writing/tests.rst

@@ -11,55 +11,148 @@ The Basics
 Unittest
 --------
 
+Unittest is the batteries-included test module in the Python standard library.
+Its API will be familiar to anyone who has used any of the JUnit/nUnit/CppUnit
+series of tools.
+
+Creating testcases is accomplished by subclassing a TestCase base class
+
+::
+
+    import unittest
+
+    def fun(x):
+        return x + 1
+
+    class MyTest(unittest.TestCase):
+        def test(self):
+            self.assertEqual(fun(3), 4)
+
+As of Python 2.7 unittest also includes its own test discovery mechanisms.
+
+    `unittest in the standard library documentation <http://docs.python.org/library/unittest.html>`_
 
 
-Doc Strings
------------
-
+Doctest
+-------
 
+The doctest module searches for pieces of text that look like interactive Python
+sessions, and then executes those sessions to verify that they work exactly as
+shown.
 
 
 Tools
 :::::
 
 
-Doctest
--------
-
-
 py.test
 -------
 
+py.test is a no-boilerplate alternative to Python's standard unittest module.
+
 ::
 
     $ pip install pytest
 
+Despite being a fully-featured and extensible test tool it boasts a simple 
+syntax. Creating a test suite is as easy as writing a module with a couple of
+functions
+
+::
+
+    # content of test_sample.py
+    def func(x):
+        return x + 1
+
+    def test_answer():
+        assert func(3) == 5
+
+and then running the `py.test` command
+
+::
+
+    $ py.test
+    =========================== test session starts ============================
+    platform darwin -- Python 2.7.1 -- pytest-2.2.1
+    collecting ... collected 1 items
+
+    test_sample.py F
+
+    ================================= FAILURES =================================
+    _______________________________ test_answer ________________________________
+
+        def test_answer():
+    >       assert func(3) == 5
+    E       assert 4 == 5
+    E        +  where 4 = func(3)
+
+    test_sample.py:5: AssertionError
+    ========================= 1 failed in 0.02 seconds =========================
+
+far less work than would be required for the equivalent functionality with the
+unittest module!
+
+    `py.test <http://pytest.org/latest/>`_
+
 
 Nose
 ----
 
-
-::
-
-    $ pip install tox
-
-
-
-Unittest2
----------
-
-A backport of Python 2.7's
+nose extends unittest to make testing easier.
 
 
 ::
 
-    $ pip install tox
+    $ pip install nose
+
+nose provides automatic test discovery to save you the hassle of manually
+creating test suites. It also provides numerous plugins for features such as
+xUnit-compatible test output, coverage reporting, and test selection.
+
+    `nose <http://readthedocs.org/docs/nose/en/latest/>`_
 
 
 tox
 ---
 
+tox is a tool for automating test environment management and testing against multiple
+interpreter configurations
 
 ::
 
     $ pip install tox
+
+tox allows you to configure complicatated multi-parameter test matrices via a
+simple ini-style configuration file.
+
+    `tox <http://tox.testrun.org/latest/>`_
+
+Unittest2
+---------
+
+unittest2 is a a backport of Python 2.7's unittest module which has an improved
+API and better assertions over the one available in previous versions of Python.
+
+If you're using Python 2.6 or below, you can install it with pip
+
+::
+
+    $ pip install unittest2
+
+You may want to import the module under the name unittest to make porting code
+to newer versions of the module easier in the future
+
+::
+
+    import unittest2 as unittest
+
+    class MyTest(unittest.TestCase):
+        ...
+
+This way if you ever switch to a newer python version and no longer need the
+unittest2 module, you can simply change the import in your test module without
+the need to change any other code.
+
+    `unittest2 <http://pypi.python.org/pypi/unittest2>`_
+
+