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

.. _`easy_install`:

**Compatibility**: Python 2.4-3.2, Jython, PyPy on Unix/Posix and Windows

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

Installation options::

    easy_install -U pytest  # or
    pip install -U pytest

To check your installation has installed the correct version::

    $ py.test --version

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


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

Let's create a small file with a test function testing a function
computes a certain value::

    # content of test_sample.py
    def func(x):
        return x + 1
    def test_answer():
        assert func(3) == 5

You can execute the test function::

    $ py.test test_sample.py
    =========================== test session starts ============================
    platform linux2 -- Python 2.6.5 -- pytest-2.0.0.dev17
    test path 1: test_sample.py
    
    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:4: AssertionError
    ========================= 1 failed in 0.02 seconds =========================

We told py.test to run the ``test_sample.py`` file and it :ref:`discovered` the 
``test_answer`` function because of the ``test_`` prefix.  We got a
failure because our little ``func(3)`` call did not return ``5``.  

.. note::

    You can simply use the `assert statement`_ for coding expectations because
    intermediate values will be presented to you.  Or to put it bluntly,
    there is no need to learn all `the JUnit legacy methods`_ for expressing
    assertions.

.. _`the 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 a certain exception is raised
--------------------------------------------------------------

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

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

    def test_mytest():
        with py.test.raises(SystemExit):
            f()

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

    $ py.test -q test_sysexit.py
    .
    1 passed in 0.01 seconds

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

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

If you start to have more than a few tests it often makes sense
to group tests logically, in classes and modules.  Let's put two
tests in a class like this::

    # 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 will be discovered because of the default `automatic test 
discovery`_.  There is no need to subclass anything.  If we now run
the module we'll see one passed and one failed test::

    $ py.test -q test_class.py
    .F
    ================================= FAILURES =================================
    ____________________________ TestClass.test_two ____________________________
    
    self = <test_class.TestClass instance at 0x1732368>
    
        def test_two(self):
            x = "hello"
    >       assert hasattr(x, 'check')
    E       assert hasattr('hello', 'check')
    
    test_class.py:8: AssertionError
    1 failed, 1 passed in 0.02 seconds

where to go from here
-------------------------------------

Here are a few suggestions where to go next:

* :ref:`cmdline` for command line invocation examples
* :ref:`good practises` for virtualenv, test layout, genscript support
* :ref:`apiref` for documentation and examples on writing Python tests

.. _`installation issues`:

Installation issues
------------------------------

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

Consult distribute_ to install the ``easy_install`` tool on your machine. 
You may also use the original but somewhat older `setuptools`_ project
although we generally recommend to use ``distribute`` because it contains
more bug fixes and also works for Python3.

For Python2 you can also consult pip_ for the popular ``pip`` tool.

However, If you want to install on Python3 you need to use Distribute_ which
provides the ``easy_install`` utility.


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
  please see here for preparing your environment for running
  command line tools: `Python for Windows`_.  You may alternatively
  use an `ActivePython install`_ which makes command line tools
  automatically available under Windows.

.. _`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 in Jython.

 :ref:`examples` for more complex examples

.. include:: links.inc