Added doctests in documentation guidelines.

docs/dev/documentation.rst

@@ -126,6 +126,43 @@ Export documentation to HTML
 
 * HTML documentation is exported to docs/_build/html/.
 
+*************
+Use doctests!
+*************
+
+This documentation uses the `Sphinx's doctest extension`_.
+
+Write doctests
+==============
+
+Here is a RST code sample to write doctests. You can find some doctests in
+:doc:`/reference/terrain`.
+
+.. highlight:: rst
+
+::
+
+  .. highlight:: python
+
+  .. doctest::
+
+     >>> print "Hello world!"
+     Hello world!
+
+See `Sphinx's doctest extension`_ and `Python's doctest`_ documentations for
+details.
+
+Run doctests
+============
+
+Go to lettuce folder and use the provided Makefile:
+
+.. highlight:: sh
+
+::
+
+  make doctests
+
 **********
 References
 **********
@@ -134,3 +171,5 @@ References
 
 .. _`Python-sphinx`: http://sphinx.pocoo.org/
 .. _`reStructuredText`: http://docutils.sourceforge.net/rst.html
+.. _`Sphinx's doctest extension`: http://sphinx.pocoo.org/ext/doctest.html#module-sphinx.ext.doctest
+.. _`Python's doctest`: http://docs.python.org/library/doctest.html