Installation and Getting Started
===================================

**Pythons**: Python 2.4-3.3, Jython, PyPy

**Platforms**: Unix/Posix and Windows

**PyPI package name**: `pytest <http://pypi.python.org/pypi/pytest>`_

**documentation as PDF**: `download latest <http://pytest.org/latest/pytest.pdf>`_

.. _`getstarted`:
.. _installation:

Installation
----------------------------------------

Installation options::

    pip install -U pytest # or
    easy_install -U pytest

To check your installation has installed the correct version::

    $ py.test --version
    This is py.test version 2.3.0, imported from /home/hpk/p/pytest/.tox/regen/local/lib/python2.7/site-packages/pytest.pyc

If you get an error checkout :ref:`installation issues`.

.. _`simpletest`:

Our first test run
----------------------------------------------------------

Let's create a first test file with a simple test function::

    # content of test_sample.py
    def func(x):
        return x + 1

    def test_answer():
        assert func(3) == 5

That's it. You can execute the test function now::

    $ py.test
    =========================== test session starts ============================
    platform linux2 -- Python 2.7.3 -- pytest-2.3.0
    collected 1 items
    
    test_sample.py F
    
    ================================= FAILURES =================================
    _______________________________ test_answer ________________________________
    
        def test_answer():
    >       assert func(3) == 5
    E       assert 4 == 5
    E        +  where 4 = func(3)
    
    test_sample.py:5: AssertionError
    ========================= 1 failed in 0.01 seconds =========================

py.test found the ``test_answer`` function by following :ref:`standard test discovery rules <test discovery>`, basically detecting the ``test_`` prefixes.  We got a failure report because our little ``func(3)`` call did not return ``5``.

.. note::

    You can simply use the ``assert`` statement for asserting test
    expectations.  pytest's :ref:`assert introspection` will intelligently
    report intermediate values of the assert expression freeing
    you from the need to learn the many names of `JUnit legacy methods`_.

.. _`JUnit legacy methods`: http://docs.python.org/library/unittest.html#test-cases

.. _`assert statement`: http://docs.python.org/reference/simple_stmts.html#the-assert-statement

Asserting that a certain exception is raised
--------------------------------------------------------------

If you want to assert that some code raises an exception you can
use the ``raises`` helper::

    # content of test_sysexit.py
    import pytest
    def f():
        raise SystemExit(1)

    def test_mytest():
        with pytest.raises(SystemExit):
            f()

Running it with, this time in "quiet" reporting mode::

    $ py.test -q test_sysexit.py
    .

.. todo:: For further ways to assert exceptions see the `raises`

Grouping multiple tests in a class
--------------------------------------------------------------

Once you start to have more than a few tests it often makes sense
to group tests logically, in classes and modules.  Let's write a class
containing two tests::

    # content of test_class.py
    class TestClass:
        def test_one(self):
            x = "this"
            assert 'h' in x

        def test_two(self):
            x = "hello"
            assert hasattr(x, 'check')

The two tests are found because of the standard :ref:`test discovery`.
There is no need to subclass anything.  We can simply
run the module by passing its filename::

    $ py.test -q test_class.py
    .F
    ================================= FAILURES =================================
    ____________________________ TestClass.test_two ____________________________
    
    self = <test_class.TestClass instance at 0x1ab56c8>
    
        def test_two(self):
            x = "hello"
    >       assert hasattr(x, 'check')
    E       assert hasattr('hello', 'check')
    
    test_class.py:8: AssertionError

The first test passed, the second failed. Again we can easily see
the intermediate values used in the assertion, helping us to
understand the reason for the failure.

Going functional: requesting a unique temporary directory
--------------------------------------------------------------

For functional tests one often needs to create some files
and pass them to application objects.  pytest provides
:ref:`builtinfixtures` which allow to request arbitrary 
resources, for example a unique temporary directory::

    # content of test_tmpdir.py
    def test_needsfiles(tmpdir):
        print tmpdir
        assert 0

We list the name ``tmpdir`` in the test function signature and
py.test will lookup and call a fixture factory to create the resource
before performing the test function call.  Let's just run it::

    $ py.test -q test_tmpdir.py
    F
    ================================= FAILURES =================================
    _____________________________ test_needsfiles ______________________________
    
    tmpdir = local('/tmp/pytest-1351/test_needsfiles0')
    
        def test_needsfiles(tmpdir):
            print tmpdir
    >       assert 0
    E       assert 0
    
    test_tmpdir.py:3: AssertionError
    ----------------------------- Captured stdout ------------------------------
    /tmp/pytest-1351/test_needsfiles0

Before the test runs, a unique-per-test-invocation temporary directory
was created.  More info at :ref:`tmpdir handling`.

You can find out what kind of builtin :ref:`fixtures` exist by typing::

    py.test --fixtures   # shows builtin and custom fixtures

Where to go next
-------------------------------------

Here are a few suggestions where to go next:

* :ref:`cmdline` for command line invocation examples
* :ref:`good practises <goodpractises>` for virtualenv, test layout, genscript support
* :ref:`apiref` for documentation and examples on using py.test
* :ref:`plugins` managing and writing plugins

.. _`installation issues`:

Known Installation issues
------------------------------

easy_install or pip not found?
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

.. _`install pip`: http://www.pip-installer.org/en/latest/index.html

`Install pip`_ for a state of the art python package installer.

Or consult `distribute docs`_ to install the ``easy_install``
tool on your machine.  

You may also use the older `setuptools`_ project but it lacks bug fixes
and does not work on Python3.

py.test not found on Windows despite installation?
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

.. _`Python for Windows`: http://www.imladris.com/Scripts/PythonForWindows.html

- **Windows**: If "easy_install" or "py.test" are not found
  you need to add the Python script path to your ``PATH``, see here:
  `Python for Windows`_.  You may alternatively use an `ActivePython install`_
  which does this for you automatically.

.. _`ActivePython install`: http://www.activestate.com/activepython/downloads

.. _`Jython does not create command line launchers`: http://bugs.jython.org/issue1491

- **Jython2.5.1 on Windows XP**: `Jython does not create command line launchers`_
  so ``py.test`` will not work correctly.  You may install py.test on
  CPython and type ``py.test --genscript=mytest`` and then use
  ``jython mytest`` to run py.test for your tests to run with Jython.

 :ref:`examples` for more complex examples

.. include:: links.inc