[1.4.x] Fixed #4501 - Documented how to use coverage.py with Django tests.

Thanks krzysiumed for the draft patch.

Backport of 7ef2781ca0ce48872e21dce2f322c9e4106d1cfd from master.

docs/topics/testing.txt

@@ -560,6 +560,49 @@ failed and erroneous tests. If all the tests pass, the return code is 0. This
 feature is useful if you're using the test-runner script in a shell script and
 need to test for success or failure at that level.
 
+Speeding up the tests
+---------------------
+
+In recent versions of Django, the default password hasher is rather slow by
+design. If during your tests you are authenticating many users, you may want
+to use a custom settings file and set the :setting:`PASSWORD_HASHERS` setting
+to a faster hashing algorithm::
+
+    PASSWORD_HASHERS = (
+        'django.contrib.auth.hashers.MD5PasswordHasher',
+    )
+
+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
 =============