# Source code for _pytest.python

    """ Python test discovery, setup and run of test functions. """
    from __future__ import absolute_import, division, print_function

    import fnmatch
    import inspect
    import sys
    import os
    import collections
    import math
    from itertools import count

    import py
    from _pytest.mark import MarkerError
    from _pytest.config import hookimpl

    import _pytest
    import _pytest._pluggy as pluggy
    from _pytest import fixtures
    from _pytest import main
    from _pytest.compat import (
        isclass, isfunction, is_generator, _escape_strings,
        REGEX_TYPE, STRING_TYPES, NoneType, NOTSET,
        get_real_func, getfslineno, safe_getattr,
        safe_str, getlocation, enum,
    )
    from _pytest.runner import fail

    cutdir1 = py.path.local(pluggy.__file__.rstrip("oc"))
    cutdir2 = py.path.local(_pytest.__file__).dirpath()
    cutdir3 = py.path.local(py.__file__).dirpath()

    def filter_traceback(entry):
        """Return True if a TracebackEntry instance should be removed from tracebacks:
        * dynamically generated code (no code to show up for it);
        * internal traceback from pytest or its internal libraries, py and pluggy.
        """
        # entry.path might sometimes return a str object when the entry
        # points to dynamically generated code
        # see https://bitbucket.org/pytest-dev/py/issues/71
        raw_filename = entry.frame.code.raw.co_filename
        is_generated = '<' in raw_filename and '>' in raw_filename
        if is_generated:
            return False
        # entry.path might point to an inexisting file, in which case it will
        # alsso return a str object. see #1133
        p = py.path.local(entry.path)
        return p != cutdir1 and not p.relto(cutdir2) and not p.relto(cutdir3)

    def pyobj_property(name):
        def get(self):
            node = self.getparent(getattr(__import__('pytest'), name))
            if node is not None:
                return node.obj
        doc = "python %s object this node was collected from (can be None)." % (
              name.lower(),)
        return property(get, None, None, doc)

    def pytest_addoption(parser):
        group = parser.getgroup("general")
        group.addoption('--fixtures', '--funcargs',
                   action="store_true", dest="showfixtures", default=False,
                   help="show available fixtures, sorted by plugin appearance")
        group.addoption(
            '--fixtures-per-test',
            action="store_true",
            dest="show_fixtures_per_test",
            default=False,
            help="show fixtures per test",
        )
        parser.addini("usefixtures", type="args", default=[],
            help="list of default fixtures to be used with this project")
        parser.addini("python_files", type="args",
            default=['test_*.py', '*_test.py'],
            help="glob-style file patterns for Python test module discovery")
        parser.addini("python_classes", type="args", default=["Test",],
            help="prefixes or glob names for Python test class discovery")
        parser.addini("python_functions", type="args", default=["test",],
            help="prefixes or glob names for Python test function and "
                 "method discovery")

        group.addoption("--import-mode", default="prepend",
            choices=["prepend", "append"], dest="importmode",
            help="prepend/append to sys.path when importing test modules, "
                 "default is to prepend.")

    def pytest_cmdline_main(config):
        if config.option.showfixtures:
            showfixtures(config)
            return 0
        if config.option.show_fixtures_per_test:
            show_fixtures_per_test(config)
            return 0

    def pytest_generate_tests(metafunc):
        # those alternative spellings are common - raise a specific error to alert
        # the user
        alt_spellings = ['parameterize', 'parametrise', 'parameterise']
        for attr in alt_spellings:
            if hasattr(metafunc.function, attr):
                msg = "{0} has '{1}', spelling should be 'parametrize'"
                raise MarkerError(msg.format(metafunc.function.__name__, attr))
        try:
            markers = metafunc.function.parametrize
        except AttributeError:
            return
        for marker in markers:
            metafunc.parametrize(*marker.args, **marker.kwargs)

    def pytest_configure(config):
        config.addinivalue_line("markers",
            "parametrize(argnames, argvalues): call a test function multiple "
            "times passing in different arguments in turn. argvalues generally "
            "needs to be a list of values if argnames specifies only one name "
            "or a list of tuples of values if argnames specifies multiple names. "
            "Example: @parametrize('arg1', [1,2]) would lead to two calls of the "
            "decorated test function, one with arg1=1 and another with arg1=2."
            "see http://pytest.org/latest/parametrize.html for more info and "
            "examples."
        )
        config.addinivalue_line("markers",
            "usefixtures(fixturename1, fixturename2, ...): mark tests as needing "
            "all of the specified fixtures. see http://pytest.org/latest/fixture.html#usefixtures "
        )

    @hookimpl(trylast=True)
    def pytest_pyfunc_call(pyfuncitem):
        testfunction = pyfuncitem.obj
        if pyfuncitem._isyieldedfunction():
            testfunction(*pyfuncitem._args)
        else:
            funcargs = pyfuncitem.funcargs
            testargs = {}
            for arg in pyfuncitem._fixtureinfo.argnames:
                testargs[arg] = funcargs[arg]
            testfunction(**testargs)
        return True

    def pytest_collect_file(path, parent):
        ext = path.ext
        if ext == ".py":
            if not parent.session.isinitpath(path):
                for pat in parent.config.getini('python_files'):
                    if path.fnmatch(pat):
                        break
                else:
                   return
            ihook = parent.session.gethookproxy(path)
            return ihook.pytest_pycollect_makemodule(path=path, parent=parent)

    def pytest_pycollect_makemodule(path, parent):
        return Module(path, parent)

    @hookimpl(hookwrapper=True)
    def pytest_pycollect_makeitem(collector, name, obj):
        outcome = yield
        res = outcome.get_result()
        if res is not None:
            return
        # nothing was collected elsewhere, let's do it here
        if isclass(obj):
            if collector.istestclass(obj, name):
                Class = collector._getcustomclass("Class")
                outcome.force_result(Class(name, parent=collector))
        elif collector.istestfunction(obj, name):
            # mock seems to store unbound methods (issue473), normalize it
            obj = getattr(obj, "__func__", obj)
            # We need to try and unwrap the function if it's a functools.partial
            # or a funtools.wrapped.
            # We musn't if it's been wrapped with mock.patch (python 2 only)
            if not (isfunction(obj) or isfunction(get_real_func(obj))):
                collector.warn(code="C2", message=
                    "cannot collect %r because it is not a function."
                    % name, )
            elif getattr(obj, "__test__", True):
                if is_generator(obj):
                    res = Generator(name, parent=collector)
                else:
                    res = list(collector._genfunctions(name, obj))
                outcome.force_result(res)

    def pytest_make_parametrize_id(config, val, argname=None):
        return None

    class PyobjContext(object):
        module = pyobj_property("Module")
        cls = pyobj_property("Class")
        instance = pyobj_property("Instance")

    class PyobjMixin(PyobjContext):
        def obj():
            def fget(self):
                obj = getattr(self, '_obj', None)
                if obj is None:
                    self._obj = obj = self._getobj()
                return obj

            def fset(self, value):
                self._obj = value

            return property(fget, fset, None, "underlying python object")

        obj = obj()

        def _getobj(self):
            return getattr(self.parent.obj, self.name)

        def getmodpath(self, stopatmodule=True, includemodule=False):
            """ return python path relative to the containing module. """
            chain = self.listchain()
            chain.reverse()
            parts = []
            for node in chain:
                if isinstance(node, Instance):
                    continue
                name = node.name
                if isinstance(node, Module):
                    name = os.path.splitext(name)[0]
                    if stopatmodule:
                        if includemodule:
                            parts.append(name)
                        break
                parts.append(name)
            parts.reverse()
            s = ".".join(parts)
            return s.replace(".[", "[")

        def _getfslineno(self):
            return getfslineno(self.obj)

        def reportinfo(self):
            # XXX caching?
            obj = self.obj
            compat_co_firstlineno = getattr(obj, 'compat_co_firstlineno', None)
            if isinstance(compat_co_firstlineno, int):
                # nose compatibility
                fspath = sys.modules[obj.__module__].__file__
                if fspath.endswith(".pyc"):
                    fspath = fspath[:-1]
                lineno = compat_co_firstlineno
            else:
                fspath, lineno = getfslineno(obj)
            modpath = self.getmodpath()
            assert isinstance(lineno, int)
            return fspath, lineno, modpath

    class PyCollector(PyobjMixin, main.Collector):

        def funcnamefilter(self, name):
            return self._matches_prefix_or_glob_option('python_functions', name)

        def isnosetest(self, obj):
            """ Look for the __test__ attribute, which is applied by the
            @nose.tools.istest decorator
            """
            # We explicitly check for "is True" here to not mistakenly treat
            # classes with a custom __getattr__ returning something truthy (like a
            # function) as test classes.
            return safe_getattr(obj, '__test__', False) is True

        def classnamefilter(self, name):
            return self._matches_prefix_or_glob_option('python_classes', name)

        def istestfunction(self, obj, name):
            return (
                (self.funcnamefilter(name) or self.isnosetest(obj)) and
                safe_getattr(obj, "__call__", False) and fixtures.getfixturemarker(obj) is None
            )

        def istestclass(self, obj, name):
            return self.classnamefilter(name) or self.isnosetest(obj)

        def _matches_prefix_or_glob_option(self, option_name, name):
            """
            checks if the given name matches the prefix or glob-pattern defined
            in ini configuration.
            """
            for option in self.config.getini(option_name):
                if name.startswith(option):
                    return True
                # check that name looks like a glob-string before calling fnmatch
                # because this is called for every name in each collected module,
                # and fnmatch is somewhat expensive to call
                elif ('*' in option or '?' in option or '[' in option) and \
                        fnmatch.fnmatch(name, option):
                    return True
            return False

        def collect(self):
            if not getattr(self.obj, "__test__", True):
                return []

            # NB. we avoid random getattrs and peek in the __dict__ instead
            # (XXX originally introduced from a PyPy need, still true?)
            dicts = [getattr(self.obj, '__dict__', {})]
            for basecls in inspect.getmro(self.obj.__class__):
                dicts.append(basecls.__dict__)
            seen = {}
            l = []
            for dic in dicts:
                for name, obj in list(dic.items()):
                    if name in seen:
                        continue
                    seen[name] = True
                    res = self.makeitem(name, obj)
                    if res is None:
                        continue
                    if not isinstance(res, list):
                        res = [res]
                    l.extend(res)
            l.sort(key=lambda item: item.reportinfo()[:2])
            return l

        def makeitem(self, name, obj):
            #assert self.ihook.fspath == self.fspath, self
            return self.ihook.pytest_pycollect_makeitem(
                collector=self, name=name, obj=obj)

        def _genfunctions(self, name, funcobj):
            module = self.getparent(Module).obj
            clscol = self.getparent(Class)
            cls = clscol and clscol.obj or None
            transfer_markers(funcobj, cls, module)
            fm = self.session._fixturemanager
            fixtureinfo = fm.getfixtureinfo(self, funcobj, cls)
            metafunc = Metafunc(funcobj, fixtureinfo, self.config,
                                cls=cls, module=module)
            methods = []
            if hasattr(module, "pytest_generate_tests"):
                methods.append(module.pytest_generate_tests)
            if hasattr(cls, "pytest_generate_tests"):
                methods.append(cls().pytest_generate_tests)
            if methods:
                self.ihook.pytest_generate_tests.call_extra(methods,
                                                            dict(metafunc=metafunc))
            else:
                self.ihook.pytest_generate_tests(metafunc=metafunc)

            Function = self._getcustomclass("Function")
            if not metafunc._calls:
                yield Function(name, parent=self, fixtureinfo=fixtureinfo)
            else:
                # add funcargs() as fixturedefs to fixtureinfo.arg2fixturedefs
                fixtures.add_funcarg_pseudo_fixture_def(self, metafunc, fm)

                for callspec in metafunc._calls:
                    subname = "%s[%s]" % (name, callspec.id)
                    yield Function(name=subname, parent=self,
                                   callspec=callspec, callobj=funcobj,
                                   fixtureinfo=fixtureinfo,
                                   keywords={callspec.id:True},
                                   originalname=name,
                                   )

    def _marked(func, mark):
        """ Returns True if :func: is already marked with :mark:, False otherwise.
        This can happen if marker is applied to class and the test file is
        invoked more than once.
        """
        try:
            func_mark = getattr(func, mark.name)
        except AttributeError:
            return False
        return mark.args == func_mark.args and mark.kwargs == func_mark.kwargs

    def transfer_markers(funcobj, cls, mod):
        # XXX this should rather be code in the mark plugin or the mark
        # plugin should merge with the python plugin.
        for holder in (cls, mod):
            try:
                pytestmark = holder.pytestmark
            except AttributeError:
                continue
            if isinstance(pytestmark, list):
                for mark in pytestmark:
                    if not _marked(funcobj, mark):
                        mark(funcobj)
            else:
                if not _marked(funcobj, pytestmark):
                    pytestmark(funcobj)

    class Module(main.File, PyCollector):
        """ Collector for test classes and functions. """

        def _getobj(self):
            return self._importtestmodule()

        def collect(self):
            self.session._fixturemanager.parsefactories(self)
            return super(Module, self).collect()

        def _importtestmodule(self):
            # we assume we are only called once per module
            importmode = self.config.getoption("--import-mode")
            try:
                mod = self.fspath.pyimport(ensuresyspath=importmode)
            except SyntaxError:
                raise self.CollectError(
                    _pytest._code.ExceptionInfo().getrepr(style="short"))
            except self.fspath.ImportMismatchError:
                e = sys.exc_info()[1]
                raise self.CollectError(
                    "import file mismatch:\n"
                    "imported module %r has this __file__ attribute:\n"
                    "  %s\n"
                    "which is not the same as the test file we want to collect:\n"
                    "  %s\n"
                    "HINT: remove __pycache__ / .pyc files and/or use a "
                    "unique basename for your test file modules"
                     % e.args
                )
            except ImportError:
                from _pytest._code.code import ExceptionInfo
                exc_info = ExceptionInfo()
                if self.config.getoption('verbose') < 2:
                    exc_info.traceback = exc_info.traceback.filter(filter_traceback)
                exc_repr = exc_info.getrepr(style='short') if exc_info.traceback else exc_info.exconly()
                formatted_tb = safe_str(exc_repr)
                raise self.CollectError(
                    "ImportError while importing test module '{fspath}'.\n"
                    "Hint: make sure your test modules/packages have valid Python names.\n"
                    "Traceback:\n"
                    "{traceback}".format(fspath=self.fspath, traceback=formatted_tb)
                )
            except _pytest.runner.Skipped as e:
                if e.allow_module_level:
                    raise
                raise self.CollectError(
                    "Using pytest.skip outside of a test is not allowed. If you are "
                    "trying to decorate a test function, use the @pytest.mark.skip "
                    "or @pytest.mark.skipif decorators instead."
                )
            self.config.pluginmanager.consider_module(mod)
            return mod

        def setup(self):
            setup_module = _get_xunit_setup_teardown(self.obj, "setUpModule")
            if setup_module is None:
                setup_module = _get_xunit_setup_teardown(self.obj, "setup_module")
            if setup_module is not None:
                setup_module()

            teardown_module = _get_xunit_setup_teardown(self.obj, 'tearDownModule')
            if teardown_module is None:
                teardown_module = _get_xunit_setup_teardown(self.obj, 'teardown_module')
            if teardown_module is not None:
                self.addfinalizer(teardown_module)

    def _get_xunit_setup_teardown(holder, attr_name, param_obj=None):
        """
        Return a callable to perform xunit-style setup or teardown if
        the function exists in the ``holder`` object.
        The ``param_obj`` parameter is the parameter which will be passed to the function
        when the callable is called without arguments, defaults to the ``holder`` object.
        Return ``None`` if a suitable callable is not found.
        """
        param_obj = param_obj if param_obj is not None else holder
        result = _get_xunit_func(holder, attr_name)
        if result is not None:
            arg_count = result.__code__.co_argcount
            if inspect.ismethod(result):
                arg_count -= 1
            if arg_count:
                return lambda: result(param_obj)
            else:
                return result

    def _get_xunit_func(obj, name):
        """Return the attribute from the given object to be used as a setup/teardown
        xunit-style function, but only if not marked as a fixture to
        avoid calling it twice.
        """
        meth = getattr(obj, name, None)
        if fixtures.getfixturemarker(meth) is None:
            return meth

    class Class(PyCollector):
        """ Collector for test methods. """
        def collect(self):
            if not safe_getattr(self.obj, "__test__", True):
                return []
            if hasinit(self.obj):
                self.warn("C1", "cannot collect test class %r because it has a "
                    "__init__ constructor" % self.obj.__name__)
                return []
            elif hasnew(self.obj):
                self.warn("C1", "cannot collect test class %r because it has a "
                                "__new__ constructor" % self.obj.__name__)
                return []
            return [self._getcustomclass("Instance")(name="()", parent=self)]

        def setup(self):
            setup_class = _get_xunit_func(self.obj, 'setup_class')
            if setup_class is not None:
                setup_class = getattr(setup_class, 'im_func', setup_class)
                setup_class = getattr(setup_class, '__func__', setup_class)
                setup_class(self.obj)

            fin_class = getattr(self.obj, 'teardown_class', None)
            if fin_class is not None:
                fin_class = getattr(fin_class, 'im_func', fin_class)
                fin_class = getattr(fin_class, '__func__', fin_class)
                self.addfinalizer(lambda: fin_class(self.obj))

    class Instance(PyCollector):
        def _getobj(self):
            return self.parent.obj()

        def collect(self):
            self.session._fixturemanager.parsefactories(self)
            return super(Instance, self).collect()

        def newinstance(self):
            self.obj = self._getobj()
            return self.obj

    class FunctionMixin(PyobjMixin):
        """ mixin for the code common to Function and Generator.
        """

        def setup(self):
            """ perform setup for this test function. """
            if hasattr(self, '_preservedparent'):
                obj = self._preservedparent
            elif isinstance(self.parent, Instance):
                obj = self.parent.newinstance()
                self.obj = self._getobj()
            else:
                obj = self.parent.obj
            if inspect.ismethod(self.obj):
                setup_name = 'setup_method'
                teardown_name = 'teardown_method'
            else:
                setup_name = 'setup_function'
                teardown_name = 'teardown_function'
            setup_func_or_method = _get_xunit_setup_teardown(obj, setup_name, param_obj=self.obj)
            if setup_func_or_method is not None:
                setup_func_or_method()
            teardown_func_or_method = _get_xunit_setup_teardown(obj, teardown_name, param_obj=self.obj)
            if teardown_func_or_method is not None:
                self.addfinalizer(teardown_func_or_method)

        def _prunetraceback(self, excinfo):
            if hasattr(self, '_obj') and not self.config.option.fulltrace:
                code = _pytest._code.Code(get_real_func(self.obj))
                path, firstlineno = code.path, code.firstlineno
                traceback = excinfo.traceback
                ntraceback = traceback.cut(path=path, firstlineno=firstlineno)
                if ntraceback == traceback:
                    ntraceback = ntraceback.cut(path=path)
                    if ntraceback == traceback:
                        #ntraceback = ntraceback.cut(excludepath=cutdir2)
                        ntraceback = ntraceback.filter(filter_traceback)
                        if not ntraceback:
                            ntraceback = traceback

                excinfo.traceback = ntraceback.filter()
                # issue364: mark all but first and last frames to
                # only show a single-line message for each frame
                if self.config.option.tbstyle == "auto":
                    if len(excinfo.traceback) > 2:
                        for entry in excinfo.traceback[1:-1]:
                            entry.set_repr_style('short')

        def _repr_failure_py(self, excinfo, style="long"):
            if excinfo.errisinstance(fail.Exception):
                if not excinfo.value.pytrace:
                    return py._builtin._totext(excinfo.value)
            return super(FunctionMixin, self)._repr_failure_py(excinfo,
                style=style)

        def repr_failure(self, excinfo, outerr=None):
            assert outerr is None, "XXX outerr usage is deprecated"
            style = self.config.option.tbstyle
            if style == "auto":
                style = "long"
            return self._repr_failure_py(excinfo, style=style)

    class Generator(FunctionMixin, PyCollector):
        def collect(self):
            # test generators are seen as collectors but they also
            # invoke setup/teardown on popular request
            # (induced by the common "test_*" naming shared with normal tests)
            from _pytest import deprecated
            self.session._setupstate.prepare(self)
            # see FunctionMixin.setup and test_setupstate_is_preserved_134
            self._preservedparent = self.parent.obj
            l = []
            seen = {}
            for i, x in enumerate(self.obj()):
                name, call, args = self.getcallargs(x)
                if not callable(call):
                    raise TypeError("%r yielded non callable test %r" %(self.obj, call,))
                if name is None:
                    name = "[%d]" % i
                else:
                    name = "['%s']" % name
                if name in seen:
                    raise ValueError("%r generated tests with non-unique name %r" %(self, name))
                seen[name] = True
                l.append(self.Function(name, self, args=args, callobj=call))
                self.config.warn('C1', deprecated.YIELD_TESTS, fslocation=self.fspath)
            return l

        def getcallargs(self, obj):
            if not isinstance(obj, (tuple, list)):
                obj = (obj,)
            # explicit naming
            if isinstance(obj[0], py.builtin._basestring):
                name = obj[0]
                obj = obj[1:]
            else:
                name = None
            call, args = obj[0], obj[1:]
            return name, call, args

    def hasinit(obj):
        init = getattr(obj, '__init__', None)
        if init:
            return init != object.__init__

    def hasnew(obj):
        new = getattr(obj, '__new__', None)
        if new:
            return new != object.__new__

    class CallSpec2(object):
        def __init__(self, metafunc):
            self.metafunc = metafunc
            self.funcargs = {}
            self._idlist = []
            self.params = {}
            self._globalid = NOTSET
            self._globalid_args = set()
            self._globalparam = NOTSET
            self._arg2scopenum = {}  # used for sorting parametrized resources
            self.keywords = {}
            self.indices = {}

        def copy(self, metafunc):
            cs = CallSpec2(self.metafunc)
            cs.funcargs.update(self.funcargs)
            cs.params.update(self.params)
            cs.keywords.update(self.keywords)
            cs.indices.update(self.indices)
            cs._arg2scopenum.update(self._arg2scopenum)
            cs._idlist = list(self._idlist)
            cs._globalid = self._globalid
            cs._globalid_args = self._globalid_args
            cs._globalparam = self._globalparam
            return cs

        def _checkargnotcontained(self, arg):
            if arg in self.params or arg in self.funcargs:
                raise ValueError("duplicate %r" %(arg,))

        def getparam(self, name):
            try:
                return self.params[name]
            except KeyError:
                if self._globalparam is NOTSET:
                    raise ValueError(name)
                return self._globalparam

        @property
        def id(self):
            return "-".join(map(str, filter(None, self._idlist)))

        def setmulti(self, valtypes, argnames, valset, id, keywords, scopenum,
                     param_index):
            for arg,val in zip(argnames, valset):
                self._checkargnotcontained(arg)
                valtype_for_arg = valtypes[arg]
                getattr(self, valtype_for_arg)[arg] = val
                self.indices[arg] = param_index
                self._arg2scopenum[arg] = scopenum
            self._idlist.append(id)
            self.keywords.update(keywords)

        def setall(self, funcargs, id, param):
            for x in funcargs:
                self._checkargnotcontained(x)
            self.funcargs.update(funcargs)
            if id is not NOTSET:
                self._idlist.append(id)
            if param is not NOTSET:
                assert self._globalparam is NOTSET
                self._globalparam = param
            for arg in funcargs:
                self._arg2scopenum[arg] = fixtures.scopenum_function

    class Metafunc(fixtures.FuncargnamesCompatAttr):
        """
        Metafunc objects are passed to the ``pytest_generate_tests`` hook.
        They help to inspect a test function and to generate tests according to
        test configuration or values specified in the class or module where a
        test function is defined.
        """
        def __init__(self, function, fixtureinfo, config, cls=None, module=None):
            #: access to the :class:`_pytest.config.Config` object for the test session
            self.config = config

            #: the module object where the test function is defined in.
            self.module = module

            #: underlying python test function
            self.function = function

            #: set of fixture names required by the test function
            self.fixturenames = fixtureinfo.names_closure

            #: class object where the test function is defined in or ``None``.
            self.cls = cls

            self._calls = []
            self._ids = py.builtin.set()
            self._arg2fixturedefs = fixtureinfo.name2fixturedefs

        def parametrize(self, argnames, argvalues, indirect=False, ids=None,
            scope=None):
            """ Add new invocations to the underlying test function using the list
            of argvalues for the given argnames.  Parametrization is performed
            during the collection phase.  If you need to setup expensive resources
            see about setting indirect to do it rather at test setup time.

            :arg argnames: a comma-separated string denoting one or more argument
                           names, or a list/tuple of argument strings.

            :arg argvalues: The list of argvalues determines how often a
                test is invoked with different argument values.  If only one
                argname was specified argvalues is a list of values.  If N
                argnames were specified, argvalues must be a list of N-tuples,
                where each tuple-element specifies a value for its respective
                argname.

            :arg indirect: The list of argnames or boolean. A list of arguments'
                names (subset of argnames). If True the list contains all names from
                the argnames. Each argvalue corresponding to an argname in this list will
                be passed as request.param to its respective argname fixture
                function so that it can perform more expensive setups during the
                setup phase of a test rather than at collection time.

            :arg ids: list of string ids, or a callable.
                If strings, each is corresponding to the argvalues so that they are
                part of the test id. If None is given as id of specific test, the
                automatically generated id for that argument will be used.
                If callable, it should take one argument (a single argvalue) and return
                a string or return None. If None, the automatically generated id for that
                argument will be used.
                If no ids are provided they will be generated automatically from
                the argvalues.

            :arg scope: if specified it denotes the scope of the parameters.
                The scope is used for grouping tests by parameter instances.
                It will also override any fixture-function defined scope, allowing
                to set a dynamic scope using test context or configuration.
            """
            from _pytest.fixtures import scope2index
            from _pytest.mark import MARK_GEN, ParameterSet
            from py.io import saferepr

            if not isinstance(argnames, (tuple, list)):
                argnames = [x.strip() for x in argnames.split(",") if x.strip()]
                force_tuple = len(argnames) == 1
            else:
                force_tuple = False
            parameters = [
                ParameterSet.extract_from(x, legacy_force_tuple=force_tuple)
                for x in argvalues]
            del argvalues

            if not parameters:
                fs, lineno = getfslineno(self.function)
                reason = "got empty parameter set %r, function %s at %s:%d" % (
                        argnames, self.function.__name__, fs, lineno)
                mark = MARK_GEN.skip(reason=reason)
                parameters.append(ParameterSet(
                    values=(NOTSET,) * len(argnames),
                    marks=[mark],
                    id=None,
                ))

            if scope is None:
                scope = _find_parametrized_scope(argnames, self._arg2fixturedefs, indirect)

            scopenum = scope2index(scope, descr='call to {0}'.format(self.parametrize))
            valtypes = {}
            for arg in argnames:
                if arg not in self.fixturenames:
                    if isinstance(indirect, (tuple, list)):
                        name = 'fixture' if arg in indirect else 'argument'
                    else:
                        name = 'fixture' if indirect else 'argument'
                    raise ValueError(
                        "%r uses no %s %r" % (
                                self.function, name, arg))

            if indirect is True:
                valtypes = dict.fromkeys(argnames, "params")
            elif indirect is False:
                valtypes = dict.fromkeys(argnames, "funcargs")
            elif isinstance(indirect, (tuple, list)):
                valtypes = dict.fromkeys(argnames, "funcargs")
                for arg in indirect:
                    if arg not in argnames:
                        raise ValueError("indirect given to %r: fixture %r doesn't exist" % (
                                         self.function, arg))
                    valtypes[arg] = "params"
            idfn = None
            if callable(ids):
                idfn = ids
                ids = None
            if ids:
                if len(ids) != len(parameters):
                    raise ValueError('%d tests specified with %d ids' % (
                                     len(parameters), len(ids)))
                for id_value in ids:
                    if id_value is not None and not isinstance(id_value, py.builtin._basestring):
                        msg = 'ids must be list of strings, found: %s (type: %s)'
                        raise ValueError(msg % (saferepr(id_value), type(id_value).__name__))
            ids = idmaker(argnames, parameters, idfn, ids, self.config)
            newcalls = []
            for callspec in self._calls or [CallSpec2(self)]:
                elements = zip(ids, parameters, count())
                for a_id, param, param_index in elements:
                    if len(param.values) != len(argnames):
                        raise ValueError(
                            'In "parametrize" the number of values ({0}) must be '
                            'equal to the number of names ({1})'.format(
                                param.values, argnames))
                    newcallspec = callspec.copy(self)
                    newcallspec.setmulti(valtypes, argnames, param.values, a_id,
                                         param.deprecated_arg_dict, scopenum, param_index)
                    newcalls.append(newcallspec)
            self._calls = newcalls

        def addcall(self, funcargs=None, id=NOTSET, param=NOTSET):
            """ (deprecated, use parametrize) Add a new call to the underlying
            test function during the collection phase of a test run.  Note that
            request.addcall() is called during the test collection phase prior and
            independently to actual test execution.  You should only use addcall()
            if you need to specify multiple arguments of a test function.

            :arg funcargs: argument keyword dictionary used when invoking
                the test function.

            :arg id: used for reporting and identification purposes.  If you
                don't supply an `id` an automatic unique id will be generated.

            :arg param: a parameter which will be exposed to a later fixture function
                invocation through the ``request.param`` attribute.
            """
            assert funcargs is None or isinstance(funcargs, dict)
            if funcargs is not None:
                for name in funcargs:
                    if name not in self.fixturenames:
                        fail("funcarg %r not used in this function." % name)
            else:
                funcargs = {}
            if id is None:
                raise ValueError("id=None not allowed")
            if id is NOTSET:
                id = len(self._calls)
            id = str(id)
            if id in self._ids:
                raise ValueError("duplicate id %r" % id)
            self._ids.add(id)

            cs = CallSpec2(self)
            cs.setall(funcargs, id, param)
            self._calls.append(cs)

    def _find_parametrized_scope(argnames, arg2fixturedefs, indirect):
        """Find the most appropriate scope for a parametrized call based on its arguments.

        When there's at least one direct argument, always use "function" scope.

        When a test function is parametrized and all its arguments are indirect
        (e.g. fixtures), return the most narrow scope based on the fixtures used.

        Related to issue #1832, based on code posted by @Kingdread.
        """
        from _pytest.fixtures import scopes
        indirect_as_list = isinstance(indirect, (list, tuple))
        all_arguments_are_fixtures = indirect is True or \
                                     indirect_as_list and len(indirect) == argnames
        if all_arguments_are_fixtures:
            fixturedefs = arg2fixturedefs or {}
            used_scopes = [fixturedef[0].scope for name, fixturedef in fixturedefs.items()]
            if used_scopes:
                # Takes the most narrow scope from used fixtures
                for scope in reversed(scopes):
                    if scope in used_scopes:
                        return scope

        return 'function'

    def _idval(val, argname, idx, idfn, config=None):
        if idfn:
            s = None
            try:
                s = idfn(val)
            except Exception:
                # See issue https://github.com/pytest-dev/pytest/issues/2169
                import warnings
                msg = "Raised while trying to determine id of parameter %s at position %d." % (argname, idx)
                msg += '\nUpdate your code as this will raise an error in pytest-4.0.'
                warnings.warn(msg, DeprecationWarning)
            if s:
                return _escape_strings(s)

        if config:
            hook_id = config.hook.pytest_make_parametrize_id(
                config=config, val=val, argname=argname)
            if hook_id:
                return hook_id

        if isinstance(val, STRING_TYPES):
            return _escape_strings(val)
        elif isinstance(val, (float, int, bool, NoneType)):
            return str(val)
        elif isinstance(val, REGEX_TYPE):
            return _escape_strings(val.pattern)
        elif enum is not None and isinstance(val, enum.Enum):
            return str(val)
        elif isclass(val) and hasattr(val, '__name__'):
            return val.__name__
        return str(argname)+str(idx)

    def _idvalset(idx, parameterset, argnames, idfn, ids, config=None):
        if parameterset.id is not None:
            return parameterset.id
        if ids is None or (idx >= len(ids) or ids[idx] is None):
            this_id = [_idval(val, argname, idx, idfn, config)
                       for val, argname in zip(parameterset.values, argnames)]
            return "-".join(this_id)
        else:
            return _escape_strings(ids[idx])

    def idmaker(argnames, parametersets, idfn=None, ids=None, config=None):
        ids = [_idvalset(valindex, parameterset, argnames, idfn, ids, config)
               for valindex, parameterset in enumerate(parametersets)]
        if len(set(ids)) != len(ids):
            # The ids are not unique
            duplicates = [testid for testid in ids if ids.count(testid) > 1]
            counters = collections.defaultdict(lambda: 0)
            for index, testid in enumerate(ids):
                if testid in duplicates:
                    ids[index] = testid + str(counters[testid])
                    counters[testid] += 1
        return ids

    def show_fixtures_per_test(config):
        from _pytest.main import wrap_session
        return wrap_session(config, _show_fixtures_per_test)

    def _show_fixtures_per_test(config, session):
        import _pytest.config
        session.perform_collect()
        curdir = py.path.local()
        tw = _pytest.config.create_terminal_writer(config)
        verbose = config.getvalue("verbose")

        def get_best_rel(func):
            loc = getlocation(func, curdir)
            return curdir.bestrelpath(loc)

        def write_fixture(fixture_def):
            argname = fixture_def.argname

            if verbose <= 0 and argname.startswith("_"):
                return
            if verbose > 0:
                bestrel = get_best_rel(fixture_def.func)
                funcargspec = "{0} -- {1}".format(argname, bestrel)
            else:
                funcargspec = argname
            tw.line(funcargspec, green=True)

            INDENT = '    {0}'
            fixture_doc = fixture_def.func.__doc__

            if fixture_doc:
                for line in fixture_doc.strip().split('\n'):
                    tw.line(INDENT.format(line.strip()))
            else:
                tw.line(INDENT.format('no docstring available'), red=True)

        def write_item(item):
            name2fixturedefs = item._fixtureinfo.name2fixturedefs

            if not name2fixturedefs:
                # The given test item does not use any fixtures
                return
            bestrel = get_best_rel(item.function)

            tw.line()
            tw.sep('-', 'fixtures used by {0}'.format(item.name))
            tw.sep('-', '({0})'.format(bestrel))
            for argname, fixture_defs in sorted(name2fixturedefs.items()):
                assert fixture_defs is not None
                if not fixture_defs:
                    continue
                # The last fixture def item in the list is expected
                # to be the one used by the test item
                write_fixture(fixture_defs[-1])

        for item in session.items:
            write_item(item)

    def showfixtures(config):
        from _pytest.main import wrap_session
        return wrap_session(config, _showfixtures_main)

    def _showfixtures_main(config, session):
        import _pytest.config
        session.perform_collect()
        curdir = py.path.local()
        tw = _pytest.config.create_terminal_writer(config)
        verbose = config.getvalue("verbose")

        fm = session._fixturemanager

        available = []
        seen = set()

        for argname, fixturedefs in fm._arg2fixturedefs.items():
            assert fixturedefs is not None
            if not fixturedefs:
                continue
            for fixturedef in fixturedefs:
                loc = getlocation(fixturedef.func, curdir)
                if (fixturedef.argname, loc) in seen:
                    continue
                seen.add((fixturedef.argname, loc))
                available.append((len(fixturedef.baseid),
                                  fixturedef.func.__module__,
                                  curdir.bestrelpath(loc),
                                  fixturedef.argname, fixturedef))

        available.sort()
        currentmodule = None
        for baseid, module, bestrel, argname, fixturedef in available:
            if currentmodule != module:
                if not module.startswith("_pytest."):
                    tw.line()
                    tw.sep("-", "fixtures defined from %s" %(module,))
                    currentmodule = module
            if verbose <= 0 and argname[0] == "_":
                continue
            if verbose > 0:
                funcargspec = "%s -- %s" %(argname, bestrel,)
            else:
                funcargspec = argname
            tw.line(funcargspec, green=True)
            loc = getlocation(fixturedef.func, curdir)
            doc = fixturedef.func.__doc__ or ""
            if doc:
                for line in doc.strip().split("\n"):
                    tw.line("    " + line.strip())
            else:
                tw.line("    %s: no docstring available" %(loc,),
                    red=True)

    # builtin pytest.raises helper

    def raises(expected_exception, *args, **kwargs):
        """
        Assert that a code block/function call raises ``expected_exception``
        and raise a failure exception otherwise.

        This helper produces a ``ExceptionInfo()`` object (see below).

        If using Python 2.5 or above, you may use this function as a
        context manager::

            >>> with raises(ZeroDivisionError):
            ...    1/0

        .. versionchanged:: 2.10

        In the context manager form you may use the keyword argument
        ``message`` to specify a custom failure message::

            >>> with raises(ZeroDivisionError, message="Expecting ZeroDivisionError"):
            ...    pass
            Traceback (most recent call last):
              ...
            Failed: Expecting ZeroDivisionError

        .. note::

           When using ``pytest.raises`` as a context manager, it's worthwhile to
           note that normal context manager rules apply and that the exception
           raised *must* be the final line in the scope of the context manager.
           Lines of code after that, within the scope of the context manager will
           not be executed. For example::

               >>> value = 15
               >>> with raises(ValueError) as exc_info:
               ...     if value > 10:
               ...         raise ValueError("value must be <= 10")
               ...     assert exc_info.type == ValueError  # this will not execute

           Instead, the following approach must be taken (note the difference in
           scope)::

               >>> with raises(ValueError) as exc_info:
               ...     if value > 10:
               ...         raise ValueError("value must be <= 10")
               ...
               >>> assert exc_info.type == ValueError

        Or you can use the keyword argument ``match`` to assert that the
        exception matches a text or regex::

            >>> with raises(ValueError, match='must be 0 or None'):
            ...     raise ValueError("value must be 0 or None")

            >>> with raises(ValueError, match=r'must be \d+$'):
            ...     raise ValueError("value must be 42")

        Or you can specify a callable by passing a to-be-called lambda::

            >>> raises(ZeroDivisionError, lambda: 1/0)
            <ExceptionInfo ...>

        or you can specify an arbitrary callable with arguments::

            >>> def f(x): return 1/x
            ...
            >>> raises(ZeroDivisionError, f, 0)
            <ExceptionInfo ...>
            >>> raises(ZeroDivisionError, f, x=0)
            <ExceptionInfo ...>

        A third possibility is to use a string to be executed::

            >>> raises(ZeroDivisionError, "f(0)")
            <ExceptionInfo ...>

        .. autoclass:: _pytest._code.ExceptionInfo
            :members:

        .. note::
            Similar to caught exception objects in Python, explicitly clearing
            local references to returned ``ExceptionInfo`` objects can
            help the Python interpreter speed up its garbage collection.

            Clearing those references breaks a reference cycle
            (``ExceptionInfo`` --> caught exception --> frame stack raising
            the exception --> current frame stack --> local variables -->
            ``ExceptionInfo``) which makes Python keep all objects referenced
            from that cycle (including all local variables in the current
            frame) alive until the next cyclic garbage collection run. See the
            official Python ``try`` statement documentation for more detailed
            information.

        """
        __tracebackhide__ = True
        msg = ("exceptions must be old-style classes or"
               " derived from BaseException, not %s")
        if isinstance(expected_exception, tuple):
            for exc in expected_exception:
                if not isclass(exc):
                    raise TypeError(msg % type(exc))
        elif not isclass(expected_exception):
            raise TypeError(msg % type(expected_exception))

        message = "DID NOT RAISE {0}".format(expected_exception)
        match_expr = None

        if not args:
            if "message" in kwargs:
                message = kwargs.pop("message")
            if "match" in kwargs:
                match_expr = kwargs.pop("match")
                message += " matching '{0}'".format(match_expr)
            return RaisesContext(expected_exception, message, match_expr)
        elif isinstance(args[0], str):
            code, = args
            assert isinstance(code, str)
            frame = sys._getframe(1)
            loc = frame.f_locals.copy()
            loc.update(kwargs)
            #print "raises frame scope: %r" % frame.f_locals
            try:
                code = _pytest._code.Source(code).compile()
                py.builtin.exec_(code, frame.f_globals, loc)
                # XXX didn'T mean f_globals == f_locals something special?
                #     this is destroyed here ...
            except expected_exception:
                return _pytest._code.ExceptionInfo()
        else:
            func = args[0]
            try:
                func(*args[1:], **kwargs)
            except expected_exception:
                return _pytest._code.ExceptionInfo()
        fail(message)

    raises.Exception = fail.Exception

    class RaisesContext(object):
        def __init__(self, expected_exception, message, match_expr):
            self.expected_exception = expected_exception
            self.message = message
            self.match_expr = match_expr
            self.excinfo = None

        def __enter__(self):
            self.excinfo = object.__new__(_pytest._code.ExceptionInfo)
            return self.excinfo

        def __exit__(self, *tp):
            __tracebackhide__ = True
            if tp[0] is None:
                fail(self.message)
            if sys.version_info < (2, 7):
                # py26: on __exit__() exc_value often does not contain the
                # exception value.
                # http://bugs.python.org/issue7853
                if not isinstance(tp[1], BaseException):
                    exc_type, value, traceback = tp
                    tp = exc_type, exc_type(value), traceback
            self.excinfo.__init__(tp)
            suppress_exception = issubclass(self.excinfo.type, self.expected_exception)
            if sys.version_info[0] == 2 and suppress_exception:
                sys.exc_clear()
            if self.match_expr:
                self.excinfo.match(self.match_expr)
            return suppress_exception

    # builtin pytest.approx helper

    class approx(object):
        """
        Assert that two numbers (or two sets of numbers) are equal to each other
        within some tolerance.

        Due to the `intricacies of floating-point arithmetic`__, numbers that we
        would intuitively expect to be equal are not always so::

            >>> 0.1 + 0.2 == 0.3
            False

        __ https://docs.python.org/3/tutorial/floatingpoint.html

        This problem is commonly encountered when writing tests, e.g. when making
        sure that floating-point values are what you expect them to be.  One way to
        deal with this problem is to assert that two floating-point numbers are
        equal to within some appropriate tolerance::

            >>> abs((0.1 + 0.2) - 0.3) < 1e-6
            True

        However, comparisons like this are tedious to write and difficult to
        understand.  Furthermore, absolute comparisons like the one above are
        usually discouraged because there's no tolerance that works well for all
        situations.  ``1e-6`` is good for numbers around ``1``, but too small for
        very big numbers and too big for very small ones.  It's better to express
        the tolerance as a fraction of the expected value, but relative comparisons
        like that are even more difficult to write correctly and concisely.

        The ``approx`` class performs floating-point comparisons using a syntax
        that's as intuitive as possible::

            >>> from pytest import approx
            >>> 0.1 + 0.2 == approx(0.3)
            True

        The same syntax also works on sequences of numbers::

            >>> (0.1 + 0.2, 0.2 + 0.4) == approx((0.3, 0.6))
            True

        By default, ``approx`` considers numbers within a relative tolerance of
        ``1e-6`` (i.e. one part in a million) of its expected value to be equal.
        This treatment would lead to surprising results if the expected value was
        ``0.0``, because nothing but ``0.0`` itself is relatively close to ``0.0``.
        To handle this case less surprisingly, ``approx`` also considers numbers
        within an absolute tolerance of ``1e-12`` of its expected value to be
        equal.  Infinite numbers are another special case.  They are only
        considered equal to themselves, regardless of the relative tolerance.  Both
        the relative and absolute tolerances can be changed by passing arguments to
        the ``approx`` constructor::

            >>> 1.0001 == approx(1)
            False
            >>> 1.0001 == approx(1, rel=1e-3)
            True
            >>> 1.0001 == approx(1, abs=1e-3)
            True

        If you specify ``abs`` but not ``rel``, the comparison will not consider
        the relative tolerance at all.  In other words, two numbers that are within
        the default relative tolerance of ``1e-6`` will still be considered unequal
        if they exceed the specified absolute tolerance.  If you specify both
        ``abs`` and ``rel``, the numbers will be considered equal if either
        tolerance is met::

            >>> 1 + 1e-8 == approx(1)
            True
            >>> 1 + 1e-8 == approx(1, abs=1e-12)
            False
            >>> 1 + 1e-8 == approx(1, rel=1e-6, abs=1e-12)
            True

        If you're thinking about using ``approx``, then you might want to know how
        it compares to other good ways of comparing floating-point numbers.  All of
        these algorithms are based on relative and absolute tolerances and should
        agree for the most part, but they do have meaningful differences:

        - ``math.isclose(a, b, rel_tol=1e-9, abs_tol=0.0)``:  True if the relative
          tolerance is met w.r.t. either ``a`` or ``b`` or if the absolute
          tolerance is met.  Because the relative tolerance is calculated w.r.t.
          both ``a`` and ``b``, this test is symmetric (i.e.  neither ``a`` nor
          ``b`` is a "reference value").  You have to specify an absolute tolerance
          if you want to compare to ``0.0`` because there is no tolerance by
          default.  Only available in python>=3.5.  `More information...`__

          __ https://docs.python.org/3/library/math.html#math.isclose

        - ``numpy.isclose(a, b, rtol=1e-5, atol=1e-8)``: True if the difference
          between ``a`` and ``b`` is less that the sum of the relative tolerance
          w.r.t. ``b`` and the absolute tolerance.  Because the relative tolerance
          is only calculated w.r.t. ``b``, this test is asymmetric and you can
          think of ``b`` as the reference value.  Support for comparing sequences
          is provided by ``numpy.allclose``.  `More information...`__

          __ http://docs.scipy.org/doc/numpy-1.10.0/reference/generated/numpy.isclose.html

        - ``unittest.TestCase.assertAlmostEqual(a, b)``: True if ``a`` and ``b``
          are within an absolute tolerance of ``1e-7``.  No relative tolerance is
          considered and the absolute tolerance cannot be changed, so this function
          is not appropriate for very large or very small numbers.  Also, it's only
          available in subclasses of ``unittest.TestCase`` and it's ugly because it
          doesn't follow PEP8.  `More information...`__

          __ https://docs.python.org/3/library/unittest.html#unittest.TestCase.assertAlmostEqual

        - ``a == pytest.approx(b, rel=1e-6, abs=1e-12)``: True if the relative
          tolerance is met w.r.t. ``b`` or if the absolute tolerance is met.
          Because the relative tolerance is only calculated w.r.t. ``b``, this test
          is asymmetric and you can think of ``b`` as the reference value.  In the
          special case that you explicitly specify an absolute tolerance but not a
          relative tolerance, only the absolute tolerance is considered.
        """

        def __init__(self, expected, rel=None, abs=None):
            self.expected = expected
            self.abs = abs
            self.rel = rel

        def __repr__(self):
            return ', '.join(repr(x) for x in self.expected)

        def __eq__(self, actual):
            from collections import Iterable
            if not isinstance(actual, Iterable):
                actual = [actual]
            if len(actual) != len(self.expected):
                return False
            return all(a == x for a, x in zip(actual, self.expected))

        __hash__ = None

        def __ne__(self, actual):
            return not (actual == self)

        @property
        def expected(self):
            # Regardless of whether the user-specified expected value is a number
            # or a sequence of numbers, return a list of ApproxNotIterable objects
            # that can be compared against.
            from collections import Iterable
            approx_non_iter = lambda x: ApproxNonIterable(x, self.rel, self.abs)
            if isinstance(self._expected, Iterable):
                return [approx_non_iter(x) for x in self._expected]
            else:
                return [approx_non_iter(self._expected)]

        @expected.setter
        def expected(self, expected):
            self._expected = expected

    class ApproxNonIterable(object):
        """
        Perform approximate comparisons for single numbers only.

        In other words, the ``expected`` attribute for objects of this class must
        be some sort of number.  This is in contrast to the ``approx`` class, where
        the ``expected`` attribute can either be a number of a sequence of numbers.
        This class is responsible for making comparisons, while ``approx`` is
        responsible for abstracting the difference between numbers and sequences of
        numbers.  Although this class can stand on its own, it's only meant to be
        used within ``approx``.
        """

        def __init__(self, expected, rel=None, abs=None):
            self.expected = expected
            self.abs = abs
            self.rel = rel

        def __repr__(self):
            if isinstance(self.expected, complex):
                return str(self.expected)

            # Infinities aren't compared using tolerances, so don't show a
            # tolerance.
            if math.isinf(self.expected):
                return str(self.expected)

            # If a sensible tolerance can't be calculated, self.tolerance will
            # raise a ValueError.  In this case, display '???'.
            try:
                vetted_tolerance = '{:.1e}'.format(self.tolerance)
            except ValueError:
                vetted_tolerance = '???'

            if sys.version_info[0] == 2:
                return '{0} +- {1}'.format(self.expected, vetted_tolerance)
            else:
                return u'{0} \u00b1 {1}'.format(self.expected, vetted_tolerance)

        def __eq__(self, actual):
            # Short-circuit exact equality.
            if actual == self.expected:
                return True

            # Infinity shouldn't be approximately equal to anything but itself, but
            # if there's a relative tolerance, it will be infinite and infinity
            # will seem approximately equal to everything.  The equal-to-itself
            # case would have been short circuited above, so here we can just
            # return false if the expected value is infinite.  The abs() call is
            # for compatibility with complex numbers.
            if math.isinf(abs(self.expected)):
                return False

            # Return true if the two numbers are within the tolerance.
            return abs(self.expected - actual) <= self.tolerance

        __hash__ = None

        def __ne__(self, actual):
            return not (actual == self)

        @property
        def tolerance(self):
            set_default = lambda x, default: x if x is not None else default

            # Figure out what the absolute tolerance should be.  ``self.abs`` is
            # either None or a value specified by the user.
            absolute_tolerance = set_default(self.abs, 1e-12)

            if absolute_tolerance < 0:
                raise ValueError("absolute tolerance can't be negative: {}".format(absolute_tolerance))
            if math.isnan(absolute_tolerance):
                raise ValueError("absolute tolerance can't be NaN.")

            # If the user specified an absolute tolerance but not a relative one,
            # just return the absolute tolerance.
            if self.rel is None:
                if self.abs is not None:
                    return absolute_tolerance

            # Figure out what the relative tolerance should be.  ``self.rel`` is
            # either None or a value specified by the user.  This is done after
            # we've made sure the user didn't ask for an absolute tolerance only,
            # because we don't want to raise errors about the relative tolerance if
            # we aren't even going to use it.
            relative_tolerance = set_default(self.rel, 1e-6) * abs(self.expected)

            if relative_tolerance < 0:
                raise ValueError("relative tolerance can't be negative: {}".format(absolute_tolerance))
            if math.isnan(relative_tolerance):
                raise ValueError("relative tolerance can't be NaN.")

            # Return the larger of the relative and absolute tolerances.
            return max(relative_tolerance, absolute_tolerance)

    #
    #  the basic pytest Function item
    #

    class Function(FunctionMixin, main.Item, fixtures.FuncargnamesCompatAttr):
        """ a Function Item is responsible for setting up and executing a
        Python test function.
        """
        _genid = None
        def __init__(self, name, parent, args=None, config=None,
                     callspec=None, callobj=NOTSET, keywords=None, session=None,
                     fixtureinfo=None, originalname=None):
            super(Function, self).__init__(name, parent, config=config,
                                           session=session)
            self._args = args
            if callobj is not NOTSET:
                self.obj = callobj

            self.keywords.update(self.obj.__dict__)
            if callspec:
                self.callspec = callspec
                self.keywords.update(callspec.keywords)
            if keywords:
                self.keywords.update(keywords)

            if fixtureinfo is None:
                fixtureinfo = self.session._fixturemanager.getfixtureinfo(
                    self.parent, self.obj, self.cls,
                    funcargs=not self._isyieldedfunction())
            self._fixtureinfo = fixtureinfo
            self.fixturenames = fixtureinfo.names_closure
            self._initrequest()

            #: original function name, without any decorations (for example
            #: parametrization adds a ``"[...]"`` suffix to function names).
            #:
            #: .. versionadded:: 3.0
            self.originalname = originalname

        def _initrequest(self):
            self.funcargs = {}
            if self._isyieldedfunction():
                assert not hasattr(self, "callspec"), (
                    "yielded functions (deprecated) cannot have funcargs")
            else:
                if hasattr(self, "callspec"):
                    callspec = self.callspec
                    assert not callspec.funcargs
                    self._genid = callspec.id
                    if hasattr(callspec, "param"):
                        self.param = callspec.param
            self._request = fixtures.FixtureRequest(self)

        @property
        def function(self):
            "underlying python 'function' object"
            return getattr(self.obj, 'im_func', self.obj)

        def _getobj(self):
            name = self.name
            i = name.find("[") # parametrization
            if i != -1:
                name = name[:i]
            return getattr(self.parent.obj, name)

        @property
        def _pyfuncitem(self):
            "(compatonly) for code expecting pytest-2.2 style request objects"
            return self

        def _isyieldedfunction(self):
            return getattr(self, "_args", None) is not None

        def runtest(self):
            """ execute the underlying test function. """
            self.ihook.pytest_pyfunc_call(pyfuncitem=self)

        def setup(self):
            super(Function, self).setup()
            fixtures.fillfixtures(self)