Changing standard (Python) test discovery

Changing directory recursion

You can set the norecursedirs option in an ini-file, for example your setup.cfg in the project root directory:

# content of setup.cfg
[pytest]
norecursedirs = .svn _build tmp*

This would tell pytest to not recurse into typical subversion or sphinx-build directories or into any tmp prefixed directory.

Changing naming conventions

You can configure different naming conventions by setting the python_files, python_classes and python_functions configuration options. Example:

# content of setup.cfg
# can also be defined in in tox.ini or pytest.ini file
[pytest]
python_files=check_*.py
python_classes=Check
python_functions=check

This would make pytest look for check_ prefixes in Python filenames, Check prefixes in classes and check prefixes in functions and classes. For example, if we have:

# content of check_myapp.py
class CheckMyApp:
    def check_simple(self):
        pass
    def check_complex(self):
        pass

then the test collection looks like this:

$ py.test --collect-only
=========================== test session starts ============================
platform linux -- Python 3.4.0 -- py-1.4.26 -- pytest-2.6.4
collected 2 items
<Module 'check_myapp.py'>
  <Class 'CheckMyApp'>
    <Instance '()'>
      <Function 'check_simple'>
      <Function 'check_complex'>

=============================  in 0.01 seconds =============================

Note

the python_functions and python_classes has no effect for unittest.TestCase test discovery because pytest delegates detection of test case methods to unittest code.

Interpreting cmdline arguments as Python packages

You can use the --pyargs option to make pytest try interpreting arguments as python package names, deriving their file system path and then running the test. For example if you have unittest2 installed you can type:

py.test --pyargs unittest2.test.test_skipping -q

which would run the respective test module. Like with other options, through an ini-file and the addopts option you can make this change more permanently:

# content of pytest.ini
[pytest]
addopts = --pyargs

Now a simple invocation of py.test NAME will check if NAME exists as an importable package/module and otherwise treat it as a filesystem path.

Finding out what is collected

You can always peek at the collection tree without running tests like this:

. $ py.test --collect-only pythoncollection.py
=========================== test session starts ============================
platform linux -- Python 3.4.0 -- py-1.4.26 -- pytest-2.6.4
collected 3 items
<Module 'pythoncollection.py'>
  <Function 'test_function'>
  <Class 'TestClass'>
    <Instance '()'>
      <Function 'test_method'>
      <Function 'test_anothermethod'>

=============================  in 0.01 seconds =============================

customizing test collection to find all .py files

You can easily instruct pytest to discover tests from every python file:

# content of pytest.ini
[pytest]
python_files = *.py

However, many projects will have a setup.py which they don’t want to be imported. Moreover, there may files only importable by a specific python version. For such cases you can dynamically define files to be ignored by listing them in a conftest.py file:

# content of conftest.py
import sys

collect_ignore = ["setup.py"]
if sys.version_info[0] > 2:
    collect_ignore.append("pkg/module_py2.py")

And then if you have a module file like this:

# content of pkg/module_py2.py
def test_only_on_python2():
    try:
        assert 0
    except Exception, e:
        pass

and a setup.py dummy file like this:

# content of setup.py
0/0  # will raise exeption if imported

then a pytest run on python2 will find the one test when run with a python2 interpreters and will leave out the setup.py file:

$ py.test --collect-only
=========================== test session starts ============================
platform linux -- Python 3.4.0 -- py-1.4.26 -- pytest-2.6.4
collected 0 items

=============================  in 0.00 seconds =============================

If you run with a Python3 interpreter the moduled added through the conftest.py file will not be considered for test collection.