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Doctests in Lino

The Developer Guide repository contains over 1000 documentation pages, many of which are tested documents.

tested document

A documentation page that contain blocks of Python code (“code snippets”) marked by a >>> in the beginning of each line, and which is getting tested using Python’s doctest command as part of a test suite.

The doctest command extracts code snippets from any text file, executes them and checks whether their output is the same as the one displayed in the document.

When you want to use doctest for testing Django code, you need to specify a Django settings module. Most tested documents use the database of some demo project. Here is an example of how you do that:

>>> from lino import startup
>>> startup('lino_book.projects.min1.settings')

Above two lines in a tested doc will trigger the site startup. They are the equivalent of starting a Django shell in the given demo project:

$ go min1
$ pm shell

In such a Django shell session you can re-play the instructions on such pages interactively (when your developer environment is installed)

The first thing you usually say in a Django shell is:

>>> from lino.api.doctest import *

How they are tested

The test suite of a repository with tested documents has a file test_docs.py in its tests directory.


The test_docs.py calls atelier.test.make_docs_suite() to automatically create a unit test for every document in the doctree. A simple test_docs.py file looks like this:

from atelier.test import make_docs_suite

def load_tests(loader, standard_tests, pattern):
    suite = make_docs_suite("docs")
    return suite

The initialization code usually imports and calls lino.startup(), then imports everything (*) from the lino.api.doctest module (which contains a selection of the most frequently used commands used in doctests).

They require of course that the demo project has been populated previously by inv prep, not on a temporary test database as the Django test runner creates it.

The advantage of this method (compared to using the Django test runner) is that they don’t need to populate the database (load the demo fixtures) for each test run. A limitation of this method is of course that they may not modify the database. That’s why we sometimes call them static or passive. They just observe whether everything looks as expected. When you want to test something that modifies the database, you don’t write a tested document but a Django test case.

See also: