Fixed #4501 - Documented how to use coverage.py with Django tests.

Thanks krzysiumed for the draft patch.

docs/topics/testing.txt

@@ -589,6 +589,34 @@ to a faster hashing algorithm::
 Don't forget to also include in :setting:`PASSWORD_HASHERS` any hashing
 algorithm used in fixtures, if any.
 
+Integration with coverage.py
+----------------------------
+
+Code coverage describes how much source code has been tested. It shows which
+parts of your code are being exercised by tests and which are not. It's an
+important part of testing applications, so it's strongly recommended to check
+the coverage of your tests.
+
+Django can be easily integrated with `coverage.py`_, a tool for measuring code
+coverage of Python programs. First, `install coverage.py`_. Next, run the
+following from your project folder containing ``manage.py``::
+
+   coverage run --source='.' manage.py test myapp
+
+This runs your tests and collects coverage data of the executed files in your
+project. You can see a report of this data by typing following command::
+
+   coverage report
+
+Note that some Django code was executed while running tests, but it is not
+listed here because of the ``source`` flag passed to the previous command.
+
+For more options like annotated HTML listings detailing missed lines, see the
+`coverage.py`_ docs.
+
+.. _coverage.py: http://nedbatchelder.com/code/coverage/
+.. _install coverage.py: http://pypi.python.org/pypi/coverage
+
 Testing tools
 =============