decorators.py

# -*- coding: utf-8 -*-
"""Decorators for labeling test objects.

Decorators that merely return a modified version of the original function
object are straightforward.  Decorators that return a new function object need
to use nose.tools.make_decorator(original_function)(decorator) in returning the
decorator, in order to preserve metadata such as function name, setup and
teardown functions and so on - see nose.tools for more information.

This module provides a set of useful decorators meant to be ready to use in
your own tests.  See the bottom of the file for the ready-made ones, and if you
find yourself writing a new one that may be of generic use, add it here.

Included decorators:


Lightweight testing that remains unittest-compatible.

- An @as_unittest decorator can be used to tag any normal parameter-less
  function as a unittest TestCase.  Then, both nose and normal unittest will
  recognize it as such.  This will make it easier to migrate away from Nose if
  we ever need/want to while maintaining very lightweight tests.

NOTE: This file contains IPython-specific decorators. Using the machinery in
IPython.external.decorators, we import either numpy.testing.decorators if numpy is
available, OR use equivalent code in IPython.external._decorators, which
we've copied verbatim from numpy.

"""

# Copyright (c) IPython Development Team.
# Distributed under the terms of the Modified BSD License.

import sys
import os
import tempfile
import unittest

from decorator import decorator

# Expose the unittest-driven decorators
from .ipunittest import ipdoctest, ipdocstring

# Grab the numpy-specific decorators which we keep in a file that we
# occasionally update from upstream: decorators.py is a copy of
# numpy.testing.decorators, we expose all of it here.
from IPython.external.decorators import *

# For onlyif_cmd_exists decorator
from IPython.utils.py3compat import string_types, which

#-----------------------------------------------------------------------------
# Classes and functions
#-----------------------------------------------------------------------------

# Simple example of the basic idea
def as_unittest(func):
    """Decorator to make a simple function into a normal test via unittest."""
    class Tester(unittest.TestCase):
        def test(self):
            func()

    Tester.__name__ = func.__name__

    return Tester

# Utility functions

def apply_wrapper(wrapper,func):
    """Apply a wrapper to a function for decoration.

    This mixes Michele Simionato's decorator tool with nose's make_decorator,
    to apply a wrapper in a decorator so that all nose attributes, as well as
    function signature and other properties, survive the decoration cleanly.
    This will ensure that wrapped functions can still be well introspected via
    IPython, for example.
    """
    import nose.tools

    return decorator(wrapper,nose.tools.make_decorator(func)(wrapper))


def make_label_dec(label,ds=None):
    """Factory function to create a decorator that applies one or more labels.

    Parameters
    ----------
      label : string or sequence
      One or more labels that will be applied by the decorator to the functions
    it decorates.  Labels are attributes of the decorated function with their
    value set to True.

      ds : string
      An optional docstring for the resulting decorator.  If not given, a
      default docstring is auto-generated.

    Returns
    -------
      A decorator.

    Examples
    --------

    A simple labeling decorator:

    >>> slow = make_label_dec('slow')
    >>> slow.__doc__
    "Labels a test as 'slow'."
    
    And one that uses multiple labels and a custom docstring:
    
    >>> rare = make_label_dec(['slow','hard'],
    ... "Mix labels 'slow' and 'hard' for rare tests.")
    >>> rare.__doc__
    "Mix labels 'slow' and 'hard' for rare tests."

    Now, let's test using this one:
    >>> @rare
    ... def f(): pass
    ...
    >>>
    >>> f.slow
    True
    >>> f.hard
    True
    """

    if isinstance(label, string_types):
        labels = [label]
    else:
        labels = label

    # Validate that the given label(s) are OK for use in setattr() by doing a
    # dry run on a dummy function.
    tmp = lambda : None
    for label in labels:
        setattr(tmp,label,True)

    # This is the actual decorator we'll return
    def decor(f):
        for label in labels:
            setattr(f,label,True)
        return f

    # Apply the user's docstring, or autogenerate a basic one
    if ds is None:
        ds = "Labels a test as %r." % label
    decor.__doc__ = ds

    return decor


# Inspired by numpy's skipif, but uses the full apply_wrapper utility to
# preserve function metadata better and allows the skip condition to be a
# callable.
def skipif(skip_condition, msg=None):
    ''' Make function raise SkipTest exception if skip_condition is true

    Parameters
    ----------

    skip_condition : bool or callable
      Flag to determine whether to skip test. If the condition is a
      callable, it is used at runtime to dynamically make the decision. This
      is useful for tests that may require costly imports, to delay the cost
      until the test suite is actually executed.
    msg : string
      Message to give on raising a SkipTest exception.

    Returns
    -------
    decorator : function
      Decorator, which, when applied to a function, causes SkipTest
      to be raised when the skip_condition was True, and the function
      to be called normally otherwise.

    Notes
    -----
    You will see from the code that we had to further decorate the
    decorator with the nose.tools.make_decorator function in order to
    transmit function name, and various other metadata.
    '''

    def skip_decorator(f):
        # Local import to avoid a hard nose dependency and only incur the
        # import time overhead at actual test-time.
        import nose

        # Allow for both boolean or callable skip conditions.
        if callable(skip_condition):
            skip_val = skip_condition
        else:
            skip_val = lambda : skip_condition

        def get_msg(func,msg=None):
            """Skip message with information about function being skipped."""
            if msg is None: out = 'Test skipped due to test condition.'
            else: out = msg
            return "Skipping test: %s. %s" % (func.__name__,out)

        # We need to define *two* skippers because Python doesn't allow both
        # return with value and yield inside the same function.
        def skipper_func(*args, **kwargs):
            """Skipper for normal test functions."""
            if skip_val():
                raise nose.SkipTest(get_msg(f,msg))
            else:
                return f(*args, **kwargs)

        def skipper_gen(*args, **kwargs):
            """Skipper for test generators."""
            if skip_val():
                raise nose.SkipTest(get_msg(f,msg))
            else:
                for x in f(*args, **kwargs):
                    yield x

        # Choose the right skipper to use when building the actual generator.
        if nose.util.isgenerator(f):
            skipper = skipper_gen
        else:
            skipper = skipper_func

        return nose.tools.make_decorator(f)(skipper)

    return skip_decorator

# A version with the condition set to true, common case just to attach a message
# to a skip decorator
def skip(msg=None):
    """Decorator factory - mark a test function for skipping from test suite.

    Parameters
    ----------
      msg : string
        Optional message to be added.

    Returns
    -------
       decorator : function
         Decorator, which, when applied to a function, causes SkipTest
         to be raised, with the optional message added.
      """

    return skipif(True,msg)


def onlyif(condition, msg):
    """The reverse from skipif, see skipif for details."""

    if callable(condition):
        skip_condition = lambda : not condition()
    else:
        skip_condition = lambda : not condition

    return skipif(skip_condition, msg)

#-----------------------------------------------------------------------------
# Utility functions for decorators
def module_not_available(module):
    """Can module be imported?  Returns true if module does NOT import.

    This is used to make a decorator to skip tests that require module to be
    available, but delay the 'import numpy' to test execution time.
    """
    try:
        mod = __import__(module)
        mod_not_avail = False
    except ImportError:
        mod_not_avail = True

    return mod_not_avail


def decorated_dummy(dec, name):
    """Return a dummy function decorated with dec, with the given name.
    
    Examples
    --------
    import IPython.testing.decorators as dec
    setup = dec.decorated_dummy(dec.skip_if_no_x11, __name__)
    """
    dummy = lambda: None
    dummy.__name__ = name
    return dec(dummy)

#-----------------------------------------------------------------------------
# Decorators for public use

# Decorators to skip certain tests on specific platforms.
skip_win32 = skipif(sys.platform == 'win32',
                    "This test does not run under Windows")
skip_linux = skipif(sys.platform.startswith('linux'),
                    "This test does not run under Linux")
skip_osx = skipif(sys.platform == 'darwin',"This test does not run under OS X")


# Decorators to skip tests if not on specific platforms.
skip_if_not_win32 = skipif(sys.platform != 'win32',
                           "This test only runs under Windows")
skip_if_not_linux = skipif(not sys.platform.startswith('linux'),
                           "This test only runs under Linux")
skip_if_not_osx = skipif(sys.platform != 'darwin',
                         "This test only runs under OSX")


_x11_skip_cond = (sys.platform not in ('darwin', 'win32') and
                  os.environ.get('DISPLAY', '') == '')
_x11_skip_msg = "Skipped under *nix when X11/XOrg not available"

skip_if_no_x11 = skipif(_x11_skip_cond, _x11_skip_msg)

# not a decorator itself, returns a dummy function to be used as setup
def skip_file_no_x11(name):
    return decorated_dummy(skip_if_no_x11, name) if _x11_skip_cond else None

# Other skip decorators

# generic skip without module
skip_without = lambda mod: skipif(module_not_available(mod), "This test requires %s" % mod)

skipif_not_numpy = skip_without('numpy')

skipif_not_matplotlib = skip_without('matplotlib')

skipif_not_sympy = skip_without('sympy')

skip_known_failure = knownfailureif(True,'This test is known to fail')

known_failure_py3 = knownfailureif(sys.version_info[0] >= 3, 
                                    'This test is known to fail on Python 3.')

# A null 'decorator', useful to make more readable code that needs to pick
# between different decorators based on OS or other conditions
null_deco = lambda f: f

# Some tests only run where we can use unicode paths. Note that we can't just
# check os.path.supports_unicode_filenames, which is always False on Linux.
try:
    f = tempfile.NamedTemporaryFile(prefix=u"tmp€")
except UnicodeEncodeError:
    unicode_paths = False
else:
    unicode_paths = True
    f.close()

onlyif_unicode_paths = onlyif(unicode_paths, ("This test is only applicable "
                                    "where we can use unicode in filenames."))


def onlyif_cmds_exist(*commands):
    """
    Decorator to skip test when at least one of `commands` is not found.
    """
    for cmd in commands:
        if not which(cmd):
            return skip("This test runs only if command '{0}' "
                        "is installed".format(cmd))
    return null_deco

def onlyif_any_cmd_exists(*commands):
    """
    Decorator to skip test unless at least one of `commands` is found.
    """
    for cmd in commands:
        if which(cmd):
            return null_deco
    return skip("This test runs only if one of the commands {0} "
                "is installed".format(commands))