test_ok1/doc/discovery.txt

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Test collection and discovery
======================================================
.. _`discovered`:
Default filesystem test discovery
-----------------------------------------------
Test collection starts from paths specified at the command line or from
the current directory. Tests are collected ahead of running the first test.
(This used to be different in earlier versions of ``py.test`` where
collection and running was interweaved which made test randomization
and distributed testing harder).
Collection nodes which have children are called "Collectors" and otherwise
they are called "Items" or "test items". Here is an example of such a
tree::
example $ py.test --collectonly test_collectonly.py
<Directory 'example'>
<Module 'test_collectonly.py'>
<Function 'test_function'>
<Class 'TestClass'>
<Instance '()'>
<Function 'test_method'>
<Function 'test_anothermethod'>
By default all directories not starting with a dot are traversed,
looking for ``test_*.py`` and ``*_test.py`` files. Those Python
files are imported under their `package name`_.
The Module collector looks for test functions
and test classes and methods. Test functions and methods
are prefixed ``test`` by default. Test classes must
start with a capitalized ``Test`` prefix.
Customizing error messages
-------------------------------------------------
On test and collection nodes ``py.test`` will invoke
the ``node.repr_failure(excinfo)`` function which
you may override and make it return an error
representation string of your choice. It
will be reported as a (red) string.