files.txt

Testing with files and directories
==================================

.. currentmodule:: testfixtures

Working with files and directories in tests can often require
excessive amounts of boilerplate code to make sure that the tests
happen in their own sandbox, files and directories contain what they
should or code processes test files correctly, and the sandbox is
cleared up at the end of the tests.

Methods of use
--------------
To help with this, TestFixtures provides the
:class:`TempDirectory` class that hides most of the
boilerplate code you would need to write.

Suppose you wanted to test the following function:

.. code-block:: python

  import os

  def foo2bar(dirpath, filename):
    path = os.path.join(dirpath, filename)
    with open(path, 'rb') as input:
        data = input.read()
    data = data.replace(b'foo', b'bar')
    with open(path, 'wb') as output:
        output.write(data)

There are several different ways depending on the type of test you are
writing:

The context manager
~~~~~~~~~~~~~~~~~~~

If you're using a version of Python where the ``with`` keyword is
available, a :class:`TempDirectory` can be used as a
context manager:

>>> from testfixtures import TempDirectory
>>> with TempDirectory() as d:
...   d.write('test.txt', b'some foo thing')
...   foo2bar(d.path, 'test.txt')
...   d.read('test.txt')
'...'
b'some bar thing'


The decorator
~~~~~~~~~~~~~

If you are working in a traditional :mod:`unittest` environment and
only work with files or directories in a particular test function, you
may find the decorator suits your needs better:

.. code-block:: python

  from testfixtures import tempdir, compare
  
  @tempdir()
  def test_function(d):
      d.write('test.txt', b'some foo thing')
      foo2bar(d.path, 'test.txt')
      compare(d.read('test.txt'), b'some bar thing')

.. check the above raises no assertion error:

  >>> test_function()

Manual usage
~~~~~~~~~~~~

If you want to work with files or directories for the duration of a
doctest or in every test in a :class:`~unittest.TestCase`, then you
can use the :class:`TempDirectory` manually.

The instantiation and replacement are done in the ``setUp`` function
of the :class:`~unittest.TestCase` or passed to the
:class:`~doctest.DocTestSuite` constructor:

>>> from testfixtures import TempDirectory
>>> d = TempDirectory()

You can then use the temporary directory for your testing:

>>> d.write('test.txt', b'some foo thing')
'...'
>>> foo2bar(d.path, 'test.txt')
>>> d.read('test.txt') == b'some bar thing'
True

Then, in the ``tearDown`` function
of the :class:`~unittest.TestCase` or passed to the
:class:`~doctest.DocTestSuite` constructor, you should make sure the
temporary directory is cleaned up:

>>> d.cleanup()

If you have multiple :class:`TempDirectory` objects in use,
you can easily clean them all up:

>>> TempDirectory.cleanup_all()

Features of a temporary directory
---------------------------------

No matter which usage pattern you pick, you will always end up with a
:class:`TempDirectory` object. These have an array of
methods that let you perform common file and directory related tasks
without all the manual boiler plate. The following sections show you
how to perform the various tasks you're likely to bump into in the
course of testing.

.. create a tempdir for the examples:

  >>> tempdir = TempDirectory()

Computing paths
~~~~~~~~~~~~~~~

If you need to know the real path of the temporary directory, the
:class:`TempDirectory` object has a :attr:`~TempDirectory.path`
attribute:

>>> tempdir.path
'...tmp...'

A common use case is to want to compute a path within the temporary
directory to pass to code under test. This can be done with the
:meth:`~TempDirectory.getpath` method:

>>> tempdir.getpath('foo').rsplit(os.sep,1)[-1]
'foo'

If you want to compute a deeper path, you can either pass either a
tuple or a forward slash-separated path:

>>> tempdir.getpath(('foo', 'baz')).rsplit(os.sep, 2)[-2:]
['foo', 'baz']
>>> tempdir.getpath('foo/baz') .rsplit(os.sep, 2)[-2:]
['foo', 'baz']

.. note:: 

  If passing a string containing path separators, a forward
  slash should be used as the separator regardless of the underlying
  platform separator.

Writing files
~~~~~~~~~~~~~

To write to a file in the root of the temporary directory, you pass
the name of the file and the content you want to write:

>>> tempdir.write('myfile.txt', b'some text')
'...'
>>> with open(os.path.join(tempdir.path, 'myfile.txt')) as f:
...     print(f.read())
some text

The full path of the newly written file is returned:

>>> path = tempdir.write('anotherfile.txt', b'some more text')
>>> with open(path) as f:
...     print(f.read())
some more text

You can also write files into a sub-directory of the temporary
directory, whether or not that directory exists, as follows:

>>> path = tempdir.write(('some', 'folder', 'afile.txt'), b'the text')
>>> with open(path) as f:
...     print(f.read())
the text

You can also specify the path to write to as a forward-slash separated
string:

>>> path = tempdir.write('some/folder/bfile.txt', b'the text')
>>> with open(path) as f:
...     print(f.read())
the text

.. note:: 

   Forward slashes should be used regardless of the file system or
   operating system in use.

Creating directories
~~~~~~~~~~~~~~~~~~~~

If you just want to create a sub-directory in the temporary directory
you can do so as follows: 

.. new tempdir:

  >>> tempdir = TempDirectory()

>>> tempdir.makedir('output')
'...'
>>> os.path.isdir(os.path.join(tempdir.path, 'output'))
True

As with file creation, the full path of the sub-directory that has
just been created is returned:

>>> path = tempdir.makedir('more_output')
>>> os.path.isdir(path)
True

Finally, you can create a nested sub-directory even if the intervening
parent directories do not exist:

>>> os.path.exists(os.path.join(tempdir.path, 'some'))
False
>>> path = tempdir.makedir(('some', 'sub', 'dir'))
>>> os.path.exists(path)
True

You can also specify the path to write to as a forward-slash separated
string:

>>> os.path.exists(os.path.join(tempdir.path, 'another'))
False
>>> path = tempdir.makedir('another/sub/dir')
>>> os.path.exists(path)
True

.. note:: 

   Forward slashes should be used regardless of the file system or
   operating system in use.

Checking the contents of files
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Once a file has been written into the temporary directory, you will
often want to check its contents. This is done with the
:meth:`TempDirectory.read` method.

Suppose the code you are testing creates some files:

.. new tempdir:

  >>> tempdir = TempDirectory()

.. code-block:: python

 def spew(path):
    with open(os.path.join(path, 'root.txt'), 'wb') as f:
        f.write(b'root output')
    os.mkdir(os.path.join(path, 'subdir'))
    with open(os.path.join(path, 'subdir', 'file.txt'), 'wb') as f:
        f.write(b'subdir output')
    os.mkdir(os.path.join(path, 'subdir', 'logs'))

We can test this function by passing it the temporary directory's path
and then using the :meth:`TempDirectory.read` method to
check the files were created with the correct content:

>>> spew(tempdir.path)
>>> tempdir.read('root.txt')
b'root output'
>>> tempdir.read(('subdir', 'file.txt'))
b'subdir output'

The second part of the above test shows how to use the
:meth:`TempDirectory.read` method to check the contents
of files that are in sub-directories of the temporary directory. This
can also be done by specifying the path relative to the root of 
the temporary directory as a forward-slash separated string:

>>> tempdir.read('subdir/file.txt')
b'subdir output'

.. note:: 

  Forward slashes should be used regardless of the file system or
  operating system in use.

Checking the contents of directories
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

It's good practice to test that your code is only writing files you expect it
to and to check they are being written to the path you expect.
:meth:`TempDirectory.compare` is the method to use to do this.

As an example, we could check that the :func:`spew` function above created no
extraneous files as follows:

>>> tempdir.compare([
...     'root.txt',
...     'subdir/',
...     'subdir/file.txt',
...     'subdir/logs/',
... ])

If we only wanted to check the sub-directory, we would specify the path to
start from, relative to the root of the temporary directory:

>>> tempdir.compare([
...     'file.txt',
...     'logs/',
... ], path='subdir')

If, like git, we only cared about files, we could do the comparison as follows:

>>> tempdir.compare([
...     'root.txt',
...     'subdir/file.txt',
... ], files_only=True)

And finally, if we only cared about files at a particular level, we could
turn off the recursive comparison as follows:

>>> tempdir.compare([
...     'root.txt',
...     'subdir',
... ], recursive=False)

The :meth:`~testfixtures.TempDirectory.compare` method can also be used to
check whether a directory contains nothing, for example:

>>> tempdir.compare(path=('subdir', 'logs'), expected=())

The above can also be done by specifying the sub-directory to be
checked as a forward-slash separated path:

>>> tempdir.compare(path='subdir/logs', expected=())

If the actual directory contents do not match the expected contents passed in,
an :class:`~exceptions.AssertionError` is raised, which will show up as a
unit test failure:

>>> tempdir.compare(['subdir'], recursive=False)
Traceback (most recent call last):
...
AssertionError: sequence not as expected:
<BLANKLINE>
same:
()
<BLANKLINE>
expected:
('subdir',)
<BLANKLINE>
actual:
('root.txt', 'subdir')

In some circumstances, you may want to ignore certain files or
sub-directories when checking contents. To make this easy, the
:class:`~testfixtures.TempDirectory` constructor takes an optional
`ignore` parameter which, if provided, should contain a sequence of
regular expressions. If any of the regular expressions return a match
when used to search through the results of any of the the methods
covered in this section, that result will be ignored.

For example, suppose we are testing some revision control code, but
don't really care about the revision control system's metadata
directories, which may or may not be present:

.. code-block:: python

  from random import choice

  def svn_ish(dirpath, filename):
    if choice((True, False)):
      os.mkdir(os.path.join(dirpath, '.svn'))
    with open(os.path.join(dirpath, filename), 'wb') as f:
      f.write(b'something')

To test this, we can use any of the previously described methods.

When used manually or as a context manager, this would be as follows:

>>> with TempDirectory(ignore=['.svn']) as d:
...   svn_ish(d.path, 'test.txt')
...   d.compare(['test.txt'])

The decorator would be as follows:

.. code-block:: python

  from testfixtures import tempdir, compare

  @tempdir(ignore=['.svn'])
  def test_function(d):
      svn_ish(d.path, 'test.txt')
      d.compare(['test.txt'])

.. check the above raises no assertion error:

  >>> test_function()


.. set things up again:

  >>> tempdir = TempDirectory()
  >>> spew(tempdir.path)

If you are working with doctests, the
:meth:`~testfixtures.TempDirectory.listdir` method can be used instead:

>>> tempdir.listdir()
root.txt
subdir
>>> tempdir.listdir('subdir')
file.txt
logs
>>> tempdir.listdir(('subdir', 'logs'))
No files or directories found.

The above example also shows how to check the contents of sub-directories of
the temporary directory and also shows what is printed when a
directory contains nothing. The
:meth:`~testfixtures.TempDirectory.listdir` method can also take a 
path separated by forward slashes, which can make doctests a little
more readable. The above test could be written as follows:

>>> tempdir.listdir('subdir/logs')
No files or directories found.

However, if you have a nested folder structure, such as that created by
our :func:`spew` function, it can be easier to just inspect the whole
tree of files and folders created. You can do this by using the
`recursive` parameter to :meth:`~testfixtures.TempDirectory.listdir`:

>>> tempdir.listdir(recursive=True)
root.txt
subdir/
subdir/file.txt
subdir/logs/

Bytes versus Strings
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. new tempdir:

  >>> tempdir = TempDirectory()

You'll notice that all of the examples so far have used raw bytes as
their data and written to and read from files only in binary mode.
This keeps all the examples nice and simple and working consistently
between Python 2 and Python 3.
One of the big changes between Python 2 and Python 3 was that the
default string type became unicode instead of binary, and a new type
for bytes was introduced. This little snippet shows the difference by
defining two constants for the British Pound symbol:

.. code-block:: python

  import sys
  PY3 = sys.version_info[:2] >= (3, 0)

  if PY3:
      some_bytes = '\xa3'.encode('utf-8')
      some_text = '\xa3'
  else:
      some_bytes = '\xc2\xa3'
      some_text = '\xc2\xa3'.decode('utf-8')

Python 3 is much stricter than Python 2 about the byte versus string
boundary and :class:`TempDirectory` has been changed to help work
with this by only reading and writing files in binary mode and
providing parameters to control decoding and encoding when you want to read and
write text.

For example, when writing, you can either write bytes directly, as we
have been in the examples so far:

>>> path = tempdir.write('currencies.txt', some_bytes)
>>> with open(path, 'rb') as currencies:
...     currencies.read()
b'\xc2\xa3'

Or, you can write text, but must specify an encoding to use when
writing the data to the file:

>>> path = tempdir.write('currencies.txt', some_text, 'utf-8')
>>> with open(path, 'rb') as currencies:
...     currencies.read()
b'\xc2\xa3'

The same is true when reading files. You can either read bytes:

>>> tempdir.read('currencies.txt') == some_bytes
True

Or, you can read text, but must specify an encoding that will be used
to decode the data in the file:

>>> tempdir.read('currencies.txt', 'utf-8') == some_text
True

Working with an existing sandbox
--------------------------------

Some testing infrastructure already provides a sandbox temporary
directory, however that infrastructure might not provide the same
level of functionality that :class:`~testfixtures.TempDirectory`
provides.

For this reason, it is possible to wrap an existing directory such as
the following with a :class:`~testfixtures.TempDirectory`:

>>> from tempfile import mkdtemp
>>> thedir = mkdtemp()

When working with the context manager, this is done as follows:

>>> with TempDirectory(path=thedir) as d:
...   d.write('file', b'data')
...   d.makedir('directory')
...   sorted(os.listdir(thedir))
'...'
'...'
['directory', 'file']

.. check thedir still exists and reset

  >>> from shutil import rmtree
  >>> os.path.exists(thedir)
  True
  >>> rmtree(thedir)
  >>> thedir = mkdtemp()

For the decorator, usage would be as follows:

.. code-block:: python

  from testfixtures import tempdir, compare
  
  @tempdir(path=thedir)
  def test_function(d):
      d.write('file', b'data')
      d.makedir('directory')
      assert sorted(os.listdir(thedir))==['directory', 'file']

.. check the above raises no assertion error and that thedir still
   exits:

  >>> test_function()
  >>> os.path.exists(thedir)
  True

It is important to note that if an existing directory is used, it will
not be deleted by either the decorator or the context manager. You
will need to make sure that the directory is cleaned up as required.

.. check the above statement is true:

  >>> os.path.exists(thedir)
  True

.. better clean it up:

 >>> rmtree(thedir)

Using with Sybil
-----------------

`Sybil`__ is a tool for testing the examples found in
documentation. It works by applying a set of specialised
parsers to the documentation and testing or otherwise using the examples
returned by those parsers.

__ http://sybil.readthedocs.io

The key differences between testing with Sybil and traditional
doctests are that it is possible to plug in different types of parser,
not just the "python console session" one, and so it is possible to
test different types of examples. TestFixtures provides one these
parsers to aid working with
:class:`~testfixtures.TempDirectory` objects. This parser makes use of
:rst:dir:`topic` directives with specific classes set to perform
different actions. 

The following sections describe how to use this parser to help with
writing temporary files and checking their contents.

Setting up
~~~~~~~~~~

To use the Sybil parser, you need to make sure a
:class:`TempDirectory` instance is available under a particular name
in the sybil test namespace. This name is then passed to the parser's
constructor and the parser is passed to the
:class:`~sybil.Sybil` constructor.

The following example shows how to use Sybil's `pytest`__ integration to
execute all of the examples below. These require not only the
TestFixtures parser but also the Sybil parsers that give more
traditional doctest behaviour, invisible code blocks
that are useful for setting things up and checking examples without
breaking up the flow of the documentation, and capturing of examples
from the documentation to use for use in other forms of testing: 

__ https://docs.pytest.org/en/latest/

.. literalinclude:: ../testfixtures/tests/conftest.py

Writing files
~~~~~~~~~~~~~

To write a file, a :rst:dir:`topic` with a class of
``write-file`` is included in the documentation. The following example
is a complete reStructuredText file that shows how to write a file
that is then used by a later example:

.. literalinclude:: ../testfixtures/tests/configparser-read.txt

Checking the contents of files
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To read a file, a :rst:dir:`topic` with a class of
``read-file`` is included in the documentation. The following example
is a complete reStructuredText file that shows how to check the values
written by the code being documented while also using this check as
part of the documentation:

.. literalinclude:: ../testfixtures/tests/configparser-write.txt

Checking the contents of directories
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

While :class:`~testfixtures.sybil.FileParser` itself does not offer any
facility for checking the contents of directories, Sybil's
:func:`~sybil.parsers.capture.parse_captures`
can be used in conjunction with the existing features of a
:class:`TempDirectory` to illustrate the contents expected
in a directory seamlessly within the documentation.

Here's a complete reStructuredText document that illustrates this
technique: 

.. literalinclude:: ../testfixtures/tests/directory-contents.txt

.. clean up all tempdirs:

  >>> TempDirectory.cleanup_all()

A note on encoding and line endings
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

As currently implemented, the parser provided by TestFixtures only works
with textual file content that can be encoded using the ASCII
character set. This content will always be written with ``'\n'`` line
separators and, when read, will always have its line endings
normalised to ``'\n'``. If you hit any limitations caused by this,
please raise an issue in the tracker on GitHub.