Testing with files and directories#

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.

To help with this, testfixtures provides the TempDirectory class that hides most of the boilerplate code you would need to write.

Methods of use#

Suppose you wanted to test the following function:

from pathlib import Path

def foo2bar(dirpath, filename):
    path = Path(dirpath) / filename
    data = path.read_bytes()
    data = data.replace(b'foo', b'bar')
    path.write_bytes(data)

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

The context manager#

A TempDirectory can be used as a context manager:

>>> from testfixtures import TempDirectory
>>> with TempDirectory() as d:
...   test_txt = (d / 'test.txt')
...   bytes_written = test_txt.write_text('some foo thing')
...   foo2bar(d.path, 'test.txt')
...   test_txt.read_bytes()
b'some bar thing'

The decorator#

If you only want to work with files or directories in a particular test function, you may find the decorator suits your needs better:

from testfixtures import tempdir, compare

@tempdir()
def test_function(root: TempDirectory):
    test_txt = root / 'test.txt'
    test_txt.write_bytes(b'some foo thing')
    foo2bar(root.path, 'test.txt')
    compare(test_txt.read_bytes(), expected=b'some bar thing')

Note

This method is not compatible with pytest’s fixture discovery stuff. Instead, put a fixture such as the following in your conftest.py:

from testfixtures import TempDirectory
import pytest

@pytest.fixture()
def root():
    with TempDirectory() as root:
        yield root

Manual usage#

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

The instantiation is done in the set-up step of the TestCase or equivalent:

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

You can then use the temporary directory for your testing:

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

Then, in the tear-down step of the TestCase or equivalent, you should make sure the temporary directory is cleaned up:

>>> d.cleanup()

The cleanup() method can also be added as an addCleanup() if that is easier or more compact in your test suite.

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

>>> TempDirectory.cleanup_all()

Working with other interfaces#

If you’re using a testing framework that already provides a temporary directory, such as pytest’s tmp_path or tmpdir, but wish to make use of the TempDirectory API for creating content or making assertions, then you can wrap the existing object as follows:

>>> with TempDirectory(tmp_path) as d:
...     d.write('some/path.txt', 'some text')
...     d.compare(expected=('some/', 'some/path.txt'))
'...'

When doing this, TempDirectory will not remove the directory it is wrapping:

>>> tmp_path.exists()
True

Inversely, if you have an existing TempDirectory but would like to interact with it using pathlib.Path objects, you can get them as follows:

>>> with TempDirectory(tmp_path) as d:
...     bytes_written = d.as_path('myfile.txt').write_text('some text')
...     d.compare(expected=['myfile.txt'])
...     d.read('myfile.txt')
b'some text'

Features of a temporary directory#

No matter which usage pattern you pick, you will always end up with a 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.

Computing paths#

If you need to know the real path of the temporary directory, the TempDirectory object has a 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 as_string() method:

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

>>> tempdir.makedir('output')
'...'
>>> (tempdir / 'output').is_dir()
True

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

>>> path = tempdir.makedir('more_output')
>>> Path(path).is_dir()
True

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

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

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

>>> (tempdir / 'another').exists()
False
>>> path = tempdir.makedir('another/sub/dir')
>>> Path(path).exists()
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 TempDirectory.read() method.

Suppose the code you are testing creates some files:

def spew(root):
     (root / 'root.txt').write_bytes(b'root output')
     (root / 'subdir').mkdir()
     (root / 'subdir' / 'file.txt').write_bytes(b'subdir output')
     (root / 'subdir' / 'logs').mkdir()

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

>>> spew(tempdir.as_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 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. TempDirectory.compare() is the method to use to do this.

As an example, we could check that the 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 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 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:

same:
()

expected:
('subdir',)

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 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:

from random import choice

def git_ish(dirpath, filename):
    root = Path(dirpath)
    if choice((True, False)):
        (root / '.git').mkdir()
    (root / filename).write_bytes(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=['.git']) as d:
...    git_ish(d.path, 'test.txt')
...    d.compare(['test.txt'])

The decorator would be as follows:

from testfixtures import tempdir, compare

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

If you are working with doctests, the 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 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 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 listdir():

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

Bytes versus Strings#

You’ll notice that all of the examples so far have only used bytes. To work with strings, TempDirectory provides explicit parameters for providing the character set to use for decoding and encoding. Using these as example, which all contain the British Pound symbol:

some_bytes = '\xa3'.encode('utf-8')
some_text = '\xa3'

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

>>> path = tempdir.write('currencies.txt', some_bytes)
>>> Path(path).read_bytes()
b'\xc2\xa3'

Or, you can write text, in which case your system default encoding, usually utf-8, will be used when writing the data to the file:

>>> path = tempdir.write('currencies.txt', some_text)
>>> Path(path).read_bytes()
b'\xc2\xa3'

Alternatively, you can specify an explicit encoding to use when writing the data to the file:

>>> latin_path = tempdir.write('latin-currencies.txt', some_text, encoding='latin1')
>>> Path(latin_path).read_bytes()
b'\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', encoding='utf-8') == some_text
True

If you’re always using a common character encoding, you can instead specify it to the constructor:

>>> tempdir = TempDirectory(encoding='utf-8')
>>> tempdir.write('more-currencies.txt', some_text)
'...'
>>> Path(path).read_bytes().decode('utf-8') == some_text
True
>>> tempdir.read('more-currencies.txt') == 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 TempDirectory provides.

For this reason, it is possible to wrap an existing directory such as the following with a 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']

For the decorator, usage would be as follows:

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']

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.

Changing the current working directory#

While it’s generally not a good idea to have software that relies on the current working directory, there’s still plenty of occasions where it ends up mattering during testing.

If you’d like the current working directory to be set to the temporary directory for the duration of a managed context, you can do it like this:

>>> import os
>>> with TempDirectory(cwd=True) as d:
...     os.getcwd() == str(d.as_path().resolve())
True

If you’d like the current working directory to be set to the temporary directory for the duration of a decorated function or context, you can do it like this:

from testfixtures import tempdir

@tempdir(cwd=True)
def test_function(d):
    assert os.getcwd() == str(d.as_path().resolve())

However, it’s better practice to only change the current working directory for the smalled context possible, and in this case it’s better to use the chdir() context manager from the standard library, available on Python 3.11 or newer:

from contextlib import chdir
from testfixtures import tempdir

@tempdir()
def test_function(d):
    assert os.getcwd() != str(d.as_path().resolve())
    ...
    with chdir(d.path):
        assert os.getcwd() == str(d.as_path().resolve())
    ...
    assert os.getcwd() != str(d.as_path().resolve())

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.

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 TempDirectory objects. This parser makes use of 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.

Note

You must be using Sybil version 6 or newer to use this parser.

Setting up#

To use the Sybil parser, you need to make sure a 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 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:

from doctest import REPORT_NDIFF, ELLIPSIS

from sybil import Sybil
from sybil.parsers.doctest import DocTestParser
from sybil.parsers.codeblock import PythonCodeBlockParser
from sybil.parsers.capture import parse_captures
from sybil.parsers.skip import skip

from testfixtures import TempDirectory
from testfixtures.sybil import FileParser


def sybil_setup(namespace):
    # _tempdir is in case it's overwritten by a test.
    namespace['tempdir'] = namespace['_tempdir'] = TempDirectory()


def sybil_teardown(namespace):
    namespace['_tempdir'].cleanup()


pytest_collect_file = Sybil(
    parsers=[
        DocTestParser(optionflags=REPORT_NDIFF|ELLIPSIS),
        PythonCodeBlockParser(),
        parse_captures,
        FileParser('tempdir'),
        skip,
    ],
    patterns=['*.txt', '*.py'],
    setup=sybil_setup, teardown=sybil_teardown,
    fixtures=['tmp_path'],
    exclude='testfixtures/tests/*.py'
).pytest()

Writing files#

To write a file, a 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:

Here's an example configuration file:

.. topic:: example.cfg
 :class: write-file

 ::

   [A Section]
   dir=frob
   long: this value continues
     on the next line

.. invisible-code-block: python
   
  # change to the temp directory
  import os
  original_dir = os.getcwd()
  os.chdir(tempdir.path)

To parse this file using the :mod:`ConfigParser` module, you would
do the following:

.. code-block:: python

   from configparser import ConfigParser
   config = ConfigParser()
   config.read('example.cfg')

The items in the section are now available as follows:

>>> for name, value in sorted(config.items('A Section')):
...     print('{0!r}:{1!r}'.format(name, value))
'dir':'frob'
'long':'this value continues\non the next line'

.. invisible-code-block: python
   
  # change out again
  import os
  os.chdir(original_dir)

Checking the contents of files#

To check the contents of a file, a topic with a class of read-file containing the expected content 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:

.. invisible-code-block: python
   
  # change to the temp directory
  import os
  original_dir = os.getcwd()
  os.chdir(tempdir.path)

To construct a configuration file using the :mod:`ConfigParser`
module, you would do the following: 

.. code-block:: python

   from configparser import ConfigParser
   config = ConfigParser()
   config.add_section('A Section')
   config.set('A Section', 'dir', 'frob')
   f = open('example.cfg','w')
   config.write(f)
   f.close()

The generated configuration file will be as follows:

.. topic:: example.cfg
 :class: read-file

 ::

   [A Section]
   dir = frob

   
.. config parser writes whitespace at the end, be careful when testing!

.. invisible-code-block: python
   
  # change out again
  import os
  os.chdir(original_dir)

Checking the contents of directories#

While FileParser itself does not offer any facility for checking the contents of directories, Sybil’s CaptureParser can be used in conjunction with the existing features of a TempDirectory to illustrate the contents expected in a directory seamlessly within the documentation.

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

Here's an example piece of code that creates some files and
directories: 

.. code-block:: python

  import os

  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'))

This function is used as follows:

>>> spew(tempdir.path)

This will create the following files and directories::

  root.txt
  subdir/
  subdir/file.txt
  subdir/logs/
 
.. -> expected_listing

.. invisible-code-block: python

  # check the listing was as expected
  tempdir.compare(expected_listing.strip().split('\n'))

A note on line endings#

As currently implemented, the parser provided by testfixtures always writes content 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.