test_ok1/doc/getting-started.txt

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

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

.. _`getstarted`:

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

Installation options::

    easy_install -U pytest  # or
    pip install -U pytest

To check your installation has installed the correct version::

    $ py.test --version
    This is py.test version 2.0.2, imported from /home/hpk/p/pytest/pytest.py
    setuptools registered plugins:
      pytest-xdist-1.6.dev2 at /home/hpk/p/pytest-xdist/xdist/plugin.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 2.6.6 -- pytest-2.0.2
    collecting ... 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 0.02 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
    expectations because intermediate values will be presented to you.
    This is arguably easier than learning all the `the JUnit legacy
    methods`_.

    However, there remains one caveat to using simple asserts: your
    assertion expression should better be side-effect free.  Because
    after an assertion failed py.test will re-evaluate the expression
    in order to present intermediate values. You will get a nice warning
    and you can easily fix it: compute the value ahead of the assert and
    then do the assertion.  Or maybe just use the assert "explicit message"
    syntax::

       assert expr, "message" # show "message" if expr is not True

.. _`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 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
    collecting ... collected 1 items
    .
    1 passed in 0.00 seconds

.. 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
    collecting ... collected 2 items
    .F
    ================================= FAILURES =================================
    ____________________________ TestClass.test_two ____________________________
    
    self = <test_class.TestClass instance at 0x24565a8>
    
        def test_two(self):
            x = "hello"
    >       assert hasattr(x, 'check')
    E       assert False
    E        +  where False = hasattr('hello', 'check')
    
    test_class.py:8: AssertionError
    1 failed, 1 passed in 0.02 seconds

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.  py.test provides
the versatile :ref:`funcarg mechanism` which allows 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 factory to create the resource
before performing the test function call.  Let's just run it::

    $ py.test -q test_tmpdir.py
    collecting ... collected 1 items
    F
    ================================= FAILURES =================================
    _____________________________ test_needsfiles ______________________________
    
    tmpdir = local('/tmp/pytest-0/test_needsfiles0')
    
        def test_needsfiles(tmpdir):
            print tmpdir
    >       assert 0
    E       assert 0
    
    test_tmpdir.py:3: AssertionError
    ----------------------------- Captured stdout ------------------------------
    /tmp/pytest-0/test_needsfiles0
    1 failed in 0.02 seconds

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:`funcargs` exist by typing::

    py.test --funcargs   # shows builtin and custom function arguments

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?
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

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.  If you use Python2 you may also install pip_.

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