# Stack-based test setUp and tearDown

Writing doctest setUp and tearDown functions can be a bit tedious, especially when setUp/tearDown functions are combined.

the zope.testing.setupstack module provides a small framework for automating test tear down. It provides a generic setUp function that sets up a stack. Normal test setUp functions call this function to set up the stack and then use the register function to register tear-down functions.

To see how this works we’ll create a faux test:

    >>> class Test:
    ...     def __init__(self):
    ...         self.globs = {}
    >>> test = Test()

We’ll register some tearDown functions that just print something:

    >>> import sys
    >>> import zope.testing.setupstack
    >>> zope.testing.setupstack.register(
    ...     test, lambda : sys.stdout.write('td 1\n'))
    >>> zope.testing.setupstack.register(
    ...     test, lambda : sys.stdout.write('td 2\n'))

Now, when we call the tearDown function:

    >>> zope.testing.setupstack.tearDown(test)
    td 2
    td 1

The registered tearDown functions are run. Note that they are run in the reverse order that they were registered.

Extra positional arguments can be passed to register:

    >>> zope.testing.setupstack.register(
    ...    test, lambda x, y, z: sys.stdout.write('%s %s %s\n' % (x, y, z)),
    ...    1, 2, z=9)
    >>> zope.testing.setupstack.tearDown(test)
    1 2 9

## Temporary Test Directory

Often, tests create files as they demonstrate functionality. They need to arrange for the removeal of these files when the test is cleaned up.

The setUpDirectory function automates this. We’ll get the current directory first:

    >>> import os
    >>> here = os.getcwd()

We’ll also create a new test:

    >>> test = Test()

Now we’ll call the setUpDirectory function:

    >>> zope.testing.setupstack.setUpDirectory(test)

We don’t have to call zope.testing.setupstack.setUp, because setUpDirectory calls it for us.

Now the current working directory has changed:

    >>> here == os.getcwd()
    False
    >>> setupstack_cwd = os.getcwd()

We can create files to out heart’s content:

    >>> foo = open('Data.fs', 'w').write('xxx')
    >>> os.path.exists(os.path.join(setupstack_cwd, 'Data.fs'))
    True

We’ll make the file read-only. This can cause problems on Windows, but setupstack takes care of that by making files writable before trying to remove them.

    >>> import stat
    >>> os.chmod('Data.fs', stat.S_IREAD)

On Unix systems, broken symlinks can cause problems because the chmod attempt by the teardown hook will fail; let’s set up a broken symlink as well, and verify the teardown doesn’t break because of that:

    >>> if hasattr(os, 'symlink'):
    ...     os.symlink('NotThere', 'BrokenLink')

When tearDown is called:

    >>> zope.testing.setupstack.tearDown(test)

We’ll be back where we started:

    >>> here == os.getcwd()
    True

and the files we created will be gone (along with the temporary directory that was created:

    >>> os.path.exists(os.path.join(setupstack_cwd, 'Data.fs'))
    False

## Context-manager support

You can leverage context managers using the `contextmanager` method. The result of calling the content manager’s __enter__ method will be returned. The context-manager’s __exit__ method will be called as part of test tear down:

    >>> class Manager(object):
    ...     def __enter__(self):
    ...         print_('enter')
    ...         return 42
    ...     def __exit__(self, *args):
    ...         print_('exit', args)

    >>> manager = Manager()
    >>> test = Test()

    >>> zope.testing.setupstack.context_manager(test, manager)
    enter
    42

    >>> zope.testing.setupstack.tearDown(test)
    exit (None, None, None)

## globs

Doctests have `globs` attributes used to hold test globals. `setupstack` was originally designed to work with doctests, but can now work with either doctests, or other test objects, as long as the test objects have either a `globs` attribute or a `__dict__` attribute. The `zope.testing.setupstack.globs` function is used to get the globals for a test object:

    >>> zope.testing.setupstack.globs(test) is test.globs
    True

Here, because the test object had a `globs` attribute, it was returned. Because we used the test object above, it has a setupstack:

    >>> '__zope.testing.setupstack' in test.globs
    True

If we remove the `globs` attribute, the object’s instance dictionary will be used:

    >>> del test.globs
    >>> zope.testing.setupstack.globs(test) is test.__dict__
    True
    >>> zope.testing.setupstack.context_manager(test, manager)
    enter
    42

    >>> '__zope.testing.setupstack' in test.__dict__
    True

The `globs` function is used internally, but can also be used by setup code to support either doctests or other test objects.