testcases.py

import difflib
import json
import posixpath
import sys
import threading
import unittest
from collections import Counter
from contextlib import contextmanager
from copy import copy
from functools import wraps
from unittest.util import safe_repr
from urllib.parse import unquote, urljoin, urlparse, urlsplit
from urllib.request import url2pathname

from django.apps import apps
from django.conf import settings
from django.core import mail
from django.core.exceptions import ValidationError
from django.core.files import locks
from django.core.handlers.wsgi import WSGIHandler, get_path_info
from django.core.management import call_command
from django.core.management.color import no_style
from django.core.management.sql import emit_post_migrate_signal
from django.core.servers.basehttp import ThreadedWSGIServer, WSGIRequestHandler
from django.db import DEFAULT_DB_ALIAS, connection, connections, transaction
from django.forms.fields import CharField
from django.http import QueryDict
from django.http.request import split_domain_port, validate_host
from django.test.client import Client
from django.test.html import HTMLParseError, parse_html
from django.test.signals import setting_changed, template_rendered
from django.test.utils import (
    CaptureQueriesContext, ContextList, compare_xml, modify_settings,
    override_settings,
)
from django.utils.decorators import classproperty
from django.views.static import serve

__all__ = ('TestCase', 'TransactionTestCase',
           'SimpleTestCase', 'skipIfDBFeature', 'skipUnlessDBFeature')


def to_list(value):
    """
    Put value into a list if it's not already one. Return an empty list if
    value is None.
    """
    if value is None:
        value = []
    elif not isinstance(value, list):
        value = [value]
    return value


def assert_and_parse_html(self, html, user_msg, msg):
    try:
        dom = parse_html(html)
    except HTMLParseError as e:
        standardMsg = '%s\n%s' % (msg, e)
        self.fail(self._formatMessage(user_msg, standardMsg))
    return dom


class _AssertNumQueriesContext(CaptureQueriesContext):
    def __init__(self, test_case, num, connection):
        self.test_case = test_case
        self.num = num
        super().__init__(connection)

    def __exit__(self, exc_type, exc_value, traceback):
        super().__exit__(exc_type, exc_value, traceback)
        if exc_type is not None:
            return
        executed = len(self)
        self.test_case.assertEqual(
            executed, self.num,
            "%d queries executed, %d expected\nCaptured queries were:\n%s" % (
                executed, self.num,
                '\n'.join(
                    '%d. %s' % (i, query['sql']) for i, query in enumerate(self.captured_queries, start=1)
                )
            )
        )


class _AssertTemplateUsedContext:
    def __init__(self, test_case, template_name):
        self.test_case = test_case
        self.template_name = template_name
        self.rendered_templates = []
        self.rendered_template_names = []
        self.context = ContextList()

    def on_template_render(self, sender, signal, template, context, **kwargs):
        self.rendered_templates.append(template)
        self.rendered_template_names.append(template.name)
        self.context.append(copy(context))

    def test(self):
        return self.template_name in self.rendered_template_names

    def message(self):
        return '%s was not rendered.' % self.template_name

    def __enter__(self):
        template_rendered.connect(self.on_template_render)
        return self

    def __exit__(self, exc_type, exc_value, traceback):
        template_rendered.disconnect(self.on_template_render)
        if exc_type is not None:
            return

        if not self.test():
            message = self.message()
            if self.rendered_templates:
                message += ' Following templates were rendered: %s' % (
                    ', '.join(self.rendered_template_names)
                )
            else:
                message += ' No template was rendered.'
            self.test_case.fail(message)


class _AssertTemplateNotUsedContext(_AssertTemplateUsedContext):
    def test(self):
        return self.template_name not in self.rendered_template_names

    def message(self):
        return '%s was rendered.' % self.template_name


class _CursorFailure:
    def __init__(self, cls_name, wrapped):
        self.cls_name = cls_name
        self.wrapped = wrapped

    def __call__(self):
        raise AssertionError(
            "Database queries aren't allowed in SimpleTestCase. "
            "Either use TestCase or TransactionTestCase to ensure proper test isolation or "
            "set %s.allow_database_queries to True to silence this failure." % self.cls_name
        )


class SimpleTestCase(unittest.TestCase):

    # The class we'll use for the test client self.client.
    # Can be overridden in derived classes.
    client_class = Client
    _overridden_settings = None
    _modified_settings = None

    # Tests shouldn't be allowed to query the database since
    # this base class doesn't enforce any isolation.
    allow_database_queries = False

    @classmethod
    def setUpClass(cls):
        super().setUpClass()
        if cls._overridden_settings:
            cls._cls_overridden_context = override_settings(**cls._overridden_settings)
            cls._cls_overridden_context.enable()
        if cls._modified_settings:
            cls._cls_modified_context = modify_settings(cls._modified_settings)
            cls._cls_modified_context.enable()
        if not cls.allow_database_queries:
            for alias in connections:
                connection = connections[alias]
                connection.cursor = _CursorFailure(cls.__name__, connection.cursor)
                connection.chunked_cursor = _CursorFailure(cls.__name__, connection.chunked_cursor)

    @classmethod
    def tearDownClass(cls):
        if not cls.allow_database_queries:
            for alias in connections:
                connection = connections[alias]
                connection.cursor = connection.cursor.wrapped
                connection.chunked_cursor = connection.chunked_cursor.wrapped
        if hasattr(cls, '_cls_modified_context'):
            cls._cls_modified_context.disable()
            delattr(cls, '_cls_modified_context')
        if hasattr(cls, '_cls_overridden_context'):
            cls._cls_overridden_context.disable()
            delattr(cls, '_cls_overridden_context')
        super().tearDownClass()

    def __call__(self, result=None):
        """
        Wrapper around default __call__ method to perform common Django test
        set up. This means that user-defined Test Cases aren't required to
        include a call to super().setUp().
        """
        testMethod = getattr(self, self._testMethodName)
        skipped = (
            getattr(self.__class__, "__unittest_skip__", False) or
            getattr(testMethod, "__unittest_skip__", False)
        )

        if not skipped:
            try:
                self._pre_setup()
            except Exception:
                result.addError(self, sys.exc_info())
                return
        super().__call__(result)
        if not skipped:
            try:
                self._post_teardown()
            except Exception:
                result.addError(self, sys.exc_info())
                return

    def _pre_setup(self):
        """
        Perform pre-test setup:
        * Create a test client.
        * Clear the mail test outbox.
        """
        self.client = self.client_class()
        mail.outbox = []

    def _post_teardown(self):
        """Perform post-test things."""
        pass

    def settings(self, **kwargs):
        """
        A context manager that temporarily sets a setting and reverts to the
        original value when exiting the context.
        """
        return override_settings(**kwargs)

    def modify_settings(self, **kwargs):
        """
        A context manager that temporarily applies changes a list setting and
        reverts back to the original value when exiting the context.
        """
        return modify_settings(**kwargs)

    def assertRedirects(self, response, expected_url, status_code=302,
                        target_status_code=200, msg_prefix='',
                        fetch_redirect_response=True):
        """
        Assert that a response redirected to a specific URL and that the
        redirect URL can be loaded.

        Won't work for external links since it uses the test client to do a
        request (use fetch_redirect_response=False to check such links without
        fetching them).
        """
        if msg_prefix:
            msg_prefix += ": "

        if hasattr(response, 'redirect_chain'):
            # The request was a followed redirect
            self.assertTrue(
                response.redirect_chain,
                msg_prefix + "Response didn't redirect as expected: Response code was %d (expected %d)"
                % (response.status_code, status_code)
            )

            self.assertEqual(
                response.redirect_chain[0][1], status_code,
                msg_prefix + "Initial response didn't redirect as expected: Response code was %d (expected %d)"
                % (response.redirect_chain[0][1], status_code)
            )

            url, status_code = response.redirect_chain[-1]
            scheme, netloc, path, query, fragment = urlsplit(url)

            self.assertEqual(
                response.status_code, target_status_code,
                msg_prefix + "Response didn't redirect as expected: Final Response code was %d (expected %d)"
                % (response.status_code, target_status_code)
            )

        else:
            # Not a followed redirect
            self.assertEqual(
                response.status_code, status_code,
                msg_prefix + "Response didn't redirect as expected: Response code was %d (expected %d)"
                % (response.status_code, status_code)
            )

            url = response.url
            scheme, netloc, path, query, fragment = urlsplit(url)

            # Prepend the request path to handle relative path redirects.
            if not path.startswith('/'):
                url = urljoin(response.request['PATH_INFO'], url)
                path = urljoin(response.request['PATH_INFO'], path)

            if fetch_redirect_response:
                # netloc might be empty, or in cases where Django tests the
                # HTTP scheme, the convention is for netloc to be 'testserver'.
                # Trust both as "internal" URLs here.
                domain, port = split_domain_port(netloc)
                if domain and not validate_host(domain, settings.ALLOWED_HOSTS):
                    raise ValueError(
                        "The test client is unable to fetch remote URLs (got %s). "
                        "If the host is served by Django, add '%s' to ALLOWED_HOSTS. "
                        "Otherwise, use assertRedirects(..., fetch_redirect_response=False)."
                        % (url, domain)
                    )
                redirect_response = response.client.get(path, QueryDict(query), secure=(scheme == 'https'))

                # Get the redirection page, using the same client that was used
                # to obtain the original response.
                self.assertEqual(
                    redirect_response.status_code, target_status_code,
                    msg_prefix + "Couldn't retrieve redirection page '%s': response code was %d (expected %d)"
                    % (path, redirect_response.status_code, target_status_code)
                )

        self.assertEqual(
            url, expected_url,
            msg_prefix + "Response redirected to '%s', expected '%s'" % (url, expected_url)
        )

    def _assert_contains(self, response, text, status_code, msg_prefix, html):
        # If the response supports deferred rendering and hasn't been rendered
        # yet, then ensure that it does get rendered before proceeding further.
        if hasattr(response, 'render') and callable(response.render) and not response.is_rendered:
            response.render()

        if msg_prefix:
            msg_prefix += ": "

        self.assertEqual(
            response.status_code, status_code,
            msg_prefix + "Couldn't retrieve content: Response code was %d"
            " (expected %d)" % (response.status_code, status_code)
        )

        if response.streaming:
            content = b''.join(response.streaming_content)
        else:
            content = response.content
        if not isinstance(text, bytes) or html:
            text = str(text)
            content = content.decode(response.charset)
            text_repr = "'%s'" % text
        else:
            text_repr = repr(text)
        if html:
            content = assert_and_parse_html(self, content, None, "Response's content is not valid HTML:")
            text = assert_and_parse_html(self, text, None, "Second argument is not valid HTML:")
        real_count = content.count(text)
        return (text_repr, real_count, msg_prefix)

    def assertContains(self, response, text, count=None, status_code=200, msg_prefix='', html=False):
        """
        Assert that a response indicates that some content was retrieved
        successfully, (i.e., the HTTP status code was as expected) and that
        ``text`` occurs ``count`` times in the content of the response.
        If ``count`` is None, the count doesn't matter - the assertion is true
        if the text occurs at least once in the response.
        """
        text_repr, real_count, msg_prefix = self._assert_contains(
            response, text, status_code, msg_prefix, html)

        if count is not None:
            self.assertEqual(
                real_count, count,
                msg_prefix + "Found %d instances of %s in response (expected %d)" % (real_count, text_repr, count)
            )
        else:
            self.assertTrue(real_count != 0, msg_prefix + "Couldn't find %s in response" % text_repr)

    def assertNotContains(self, response, text, status_code=200, msg_prefix='', html=False):
        """
        Assert that a response indicates that some content was retrieved
        successfully, (i.e., the HTTP status code was as expected) and that
        ``text`` doesn't occurs in the content of the response.
        """
        text_repr, real_count, msg_prefix = self._assert_contains(
            response, text, status_code, msg_prefix, html)

        self.assertEqual(real_count, 0, msg_prefix + "Response should not contain %s" % text_repr)

    def assertFormError(self, response, form, field, errors, msg_prefix=''):
        """
        Assert that a form used to render the response has a specific field
        error.
        """
        if msg_prefix:
            msg_prefix += ": "

        # Put context(s) into a list to simplify processing.
        contexts = to_list(response.context)
        if not contexts:
            self.fail(msg_prefix + "Response did not use any contexts to render the response")

        # Put error(s) into a list to simplify processing.
        errors = to_list(errors)

        # Search all contexts for the error.
        found_form = False
        for i, context in enumerate(contexts):
            if form not in context:
                continue
            found_form = True
            for err in errors:
                if field:
                    if field in context[form].errors:
                        field_errors = context[form].errors[field]
                        self.assertTrue(
                            err in field_errors,
                            msg_prefix + "The field '%s' on form '%s' in"
                            " context %d does not contain the error '%s'"
                            " (actual errors: %s)" %
                            (field, form, i, err, repr(field_errors))
                        )
                    elif field in context[form].fields:
                        self.fail(
                            msg_prefix + "The field '%s' on form '%s' in context %d contains no errors" %
                            (field, form, i)
                        )
                    else:
                        self.fail(
                            msg_prefix + "The form '%s' in context %d does not contain the field '%s'" %
                            (form, i, field)
                        )
                else:
                    non_field_errors = context[form].non_field_errors()
                    self.assertTrue(
                        err in non_field_errors,
                        msg_prefix + "The form '%s' in context %d does not"
                        " contain the non-field error '%s'"
                        " (actual errors: %s)" %
                        (form, i, err, non_field_errors or 'none')
                    )
        if not found_form:
            self.fail(msg_prefix + "The form '%s' was not used to render the response" % form)

    def assertFormsetError(self, response, formset, form_index, field, errors,
                           msg_prefix=''):
        """
        Assert that a formset used to render the response has a specific error.

        For field errors, specify the ``form_index`` and the ``field``.
        For non-field errors, specify the ``form_index`` and the ``field`` as
        None.
        For non-form errors, specify ``form_index`` as None and the ``field``
        as None.
        """
        # Add punctuation to msg_prefix
        if msg_prefix:
            msg_prefix += ": "

        # Put context(s) into a list to simplify processing.
        contexts = to_list(response.context)
        if not contexts:
            self.fail(msg_prefix + 'Response did not use any contexts to '
                      'render the response')

        # Put error(s) into a list to simplify processing.
        errors = to_list(errors)

        # Search all contexts for the error.
        found_formset = False
        for i, context in enumerate(contexts):
            if formset not in context:
                continue
            found_formset = True
            for err in errors:
                if field is not None:
                    if field in context[formset].forms[form_index].errors:
                        field_errors = context[formset].forms[form_index].errors[field]
                        self.assertTrue(
                            err in field_errors,
                            msg_prefix + "The field '%s' on formset '%s', "
                            "form %d in context %d does not contain the "
                            "error '%s' (actual errors: %s)" %
                            (field, formset, form_index, i, err, repr(field_errors))
                        )
                    elif field in context[formset].forms[form_index].fields:
                        self.fail(
                            msg_prefix + "The field '%s' on formset '%s', form %d in context %d contains no errors"
                            % (field, formset, form_index, i)
                        )
                    else:
                        self.fail(
                            msg_prefix + "The formset '%s', form %d in context %d does not contain the field '%s'"
                            % (formset, form_index, i, field)
                        )
                elif form_index is not None:
                    non_field_errors = context[formset].forms[form_index].non_field_errors()
                    self.assertFalse(
                        not non_field_errors,
                        msg_prefix + "The formset '%s', form %d in context %d "
                        "does not contain any non-field errors." % (formset, form_index, i)
                    )
                    self.assertTrue(
                        err in non_field_errors,
                        msg_prefix + "The formset '%s', form %d in context %d "
                        "does not contain the non-field error '%s' (actual errors: %s)"
                        % (formset, form_index, i, err, repr(non_field_errors))
                    )
                else:
                    non_form_errors = context[formset].non_form_errors()
                    self.assertFalse(
                        not non_form_errors,
                        msg_prefix + "The formset '%s' in context %d does not "
                        "contain any non-form errors." % (formset, i)
                    )
                    self.assertTrue(
                        err in non_form_errors,
                        msg_prefix + "The formset '%s' in context %d does not "
                        "contain the non-form error '%s' (actual errors: %s)"
                        % (formset, i, err, repr(non_form_errors))
                    )
        if not found_formset:
            self.fail(msg_prefix + "The formset '%s' was not used to render the response" % formset)

    def _assert_template_used(self, response, template_name, msg_prefix):

        if response is None and template_name is None:
            raise TypeError('response and/or template_name argument must be provided')

        if msg_prefix:
            msg_prefix += ": "

        if template_name is not None and response is not None and not hasattr(response, 'templates'):
            raise ValueError(
                "assertTemplateUsed() and assertTemplateNotUsed() are only "
                "usable on responses fetched using the Django test Client."
            )

        if not hasattr(response, 'templates') or (response is None and template_name):
            if response:
                template_name = response
                response = None
            # use this template with context manager
            return template_name, None, msg_prefix

        template_names = [t.name for t in response.templates if t.name is not None]
        return None, template_names, msg_prefix

    def assertTemplateUsed(self, response=None, template_name=None, msg_prefix='', count=None):
        """
        Assert that the template with the provided name was used in rendering
        the response. Also usable as context manager.
        """
        context_mgr_template, template_names, msg_prefix = self._assert_template_used(
            response, template_name, msg_prefix)

        if context_mgr_template:
            # Use assertTemplateUsed as context manager.
            return _AssertTemplateUsedContext(self, context_mgr_template)

        if not template_names:
            self.fail(msg_prefix + "No templates used to render the response")
        self.assertTrue(
            template_name in template_names,
            msg_prefix + "Template '%s' was not a template used to render"
            " the response. Actual template(s) used: %s"
            % (template_name, ', '.join(template_names))
        )

        if count is not None:
            self.assertEqual(
                template_names.count(template_name), count,
                msg_prefix + "Template '%s' was expected to be rendered %d "
                "time(s) but was actually rendered %d time(s)."
                % (template_name, count, template_names.count(template_name))
            )

    def assertTemplateNotUsed(self, response=None, template_name=None, msg_prefix=''):
        """
        Assert that the template with the provided name was NOT used in
        rendering the response. Also usable as context manager.
        """
        context_mgr_template, template_names, msg_prefix = self._assert_template_used(
            response, template_name, msg_prefix
        )
        if context_mgr_template:
            # Use assertTemplateNotUsed as context manager.
            return _AssertTemplateNotUsedContext(self, context_mgr_template)

        self.assertFalse(
            template_name in template_names,
            msg_prefix + "Template '%s' was used unexpectedly in rendering the response" % template_name
        )

    @contextmanager
    def _assert_raises_or_warns_cm(self, func, cm_attr, expected_exception, expected_message):
        with func(expected_exception) as cm:
            yield cm
        self.assertIn(expected_message, str(getattr(cm, cm_attr)))

    def _assertFooMessage(self, func, cm_attr, expected_exception, expected_message, *args, **kwargs):
        callable_obj = None
        if args:
            callable_obj = args[0]
            args = args[1:]
        cm = self._assert_raises_or_warns_cm(func, cm_attr, expected_exception, expected_message)
        # Assertion used in context manager fashion.
        if callable_obj is None:
            return cm
        # Assertion was passed a callable.
        with cm:
            callable_obj(*args, **kwargs)

    def assertRaisesMessage(self, expected_exception, expected_message, *args, **kwargs):
        """
        Assert that expected_message is found in the message of a raised
        exception.

        Args:
            expected_exception: Exception class expected to be raised.
            expected_message: expected error message string value.
            args: Function to be called and extra positional args.
            kwargs: Extra kwargs.
        """
        return self._assertFooMessage(
            self.assertRaises, 'exception', expected_exception, expected_message,
            *args, **kwargs
        )

    def assertWarnsMessage(self, expected_warning, expected_message, *args, **kwargs):
        """
        Same as assertRaisesMessage but for assertWarns() instead of
        assertRaises().
        """
        return self._assertFooMessage(
            self.assertWarns, 'warning', expected_warning, expected_message,
            *args, **kwargs
        )

    def assertFieldOutput(self, fieldclass, valid, invalid, field_args=None,
                          field_kwargs=None, empty_value=''):
        """
        Assert that a form field behaves correctly with various inputs.

        Args:
            fieldclass: the class of the field to be tested.
            valid: a dictionary mapping valid inputs to their expected
                    cleaned values.
            invalid: a dictionary mapping invalid inputs to one or more
                    raised error messages.
            field_args: the args passed to instantiate the field
            field_kwargs: the kwargs passed to instantiate the field
            empty_value: the expected clean output for inputs in empty_values
        """
        if field_args is None:
            field_args = []
        if field_kwargs is None:
            field_kwargs = {}
        required = fieldclass(*field_args, **field_kwargs)
        optional = fieldclass(*field_args, **{**field_kwargs, 'required': False})
        # test valid inputs
        for input, output in valid.items():
            self.assertEqual(required.clean(input), output)
            self.assertEqual(optional.clean(input), output)
        # test invalid inputs
        for input, errors in invalid.items():
            with self.assertRaises(ValidationError) as context_manager:
                required.clean(input)
            self.assertEqual(context_manager.exception.messages, errors)

            with self.assertRaises(ValidationError) as context_manager:
                optional.clean(input)
            self.assertEqual(context_manager.exception.messages, errors)
        # test required inputs
        error_required = [required.error_messages['required']]
        for e in required.empty_values:
            with self.assertRaises(ValidationError) as context_manager:
                required.clean(e)
            self.assertEqual(context_manager.exception.messages, error_required)
            self.assertEqual(optional.clean(e), empty_value)
        # test that max_length and min_length are always accepted
        if issubclass(fieldclass, CharField):
            field_kwargs.update({'min_length': 2, 'max_length': 20})
            self.assertIsInstance(fieldclass(*field_args, **field_kwargs), fieldclass)

    def assertHTMLEqual(self, html1, html2, msg=None):
        """
        Assert that two HTML snippets are semantically the same.
        Whitespace in most cases is ignored, and attribute ordering is not
        significant. The arguments must be valid HTML.
        """
        dom1 = assert_and_parse_html(self, html1, msg, 'First argument is not valid HTML:')
        dom2 = assert_and_parse_html(self, html2, msg, 'Second argument is not valid HTML:')

        if dom1 != dom2:
            standardMsg = '%s != %s' % (
                safe_repr(dom1, True), safe_repr(dom2, True))
            diff = ('\n' + '\n'.join(difflib.ndiff(
                str(dom1).splitlines(), str(dom2).splitlines(),
            )))
            standardMsg = self._truncateMessage(standardMsg, diff)
            self.fail(self._formatMessage(msg, standardMsg))

    def assertHTMLNotEqual(self, html1, html2, msg=None):
        """Assert that two HTML snippets are not semantically equivalent."""
        dom1 = assert_and_parse_html(self, html1, msg, 'First argument is not valid HTML:')
        dom2 = assert_and_parse_html(self, html2, msg, 'Second argument is not valid HTML:')

        if dom1 == dom2:
            standardMsg = '%s == %s' % (
                safe_repr(dom1, True), safe_repr(dom2, True))
            self.fail(self._formatMessage(msg, standardMsg))

    def assertInHTML(self, needle, haystack, count=None, msg_prefix=''):
        needle = assert_and_parse_html(self, needle, None, 'First argument is not valid HTML:')
        haystack = assert_and_parse_html(self, haystack, None, 'Second argument is not valid HTML:')
        real_count = haystack.count(needle)
        if count is not None:
            self.assertEqual(
                real_count, count,
                msg_prefix + "Found %d instances of '%s' in response (expected %d)" % (real_count, needle, count)
            )
        else:
            self.assertTrue(real_count != 0, msg_prefix + "Couldn't find '%s' in response" % needle)

    def assertJSONEqual(self, raw, expected_data, msg=None):
        """
        Assert that the JSON fragments raw and expected_data are equal.
        Usual JSON non-significant whitespace rules apply as the heavyweight
        is delegated to the json library.
        """
        try:
            data = json.loads(raw)
        except json.JSONDecodeError:
            self.fail("First argument is not valid JSON: %r" % raw)
        if isinstance(expected_data, str):
            try:
                expected_data = json.loads(expected_data)
            except ValueError:
                self.fail("Second argument is not valid JSON: %r" % expected_data)
        self.assertEqual(data, expected_data, msg=msg)

    def assertJSONNotEqual(self, raw, expected_data, msg=None):
        """
        Assert that the JSON fragments raw and expected_data are not equal.
        Usual JSON non-significant whitespace rules apply as the heavyweight
        is delegated to the json library.
        """
        try:
            data = json.loads(raw)
        except json.JSONDecodeError:
            self.fail("First argument is not valid JSON: %r" % raw)
        if isinstance(expected_data, str):
            try:
                expected_data = json.loads(expected_data)
            except json.JSONDecodeError:
                self.fail("Second argument is not valid JSON: %r" % expected_data)
        self.assertNotEqual(data, expected_data, msg=msg)

    def assertXMLEqual(self, xml1, xml2, msg=None):
        """
        Assert that two XML snippets are semantically the same.
        Whitespace in most cases is ignored and attribute ordering is not
        significant. The arguments must be valid XML.
        """
        try:
            result = compare_xml(xml1, xml2)
        except Exception as e:
            standardMsg = 'First or second argument is not valid XML\n%s' % e
            self.fail(self._formatMessage(msg, standardMsg))
        else:
            if not result:
                standardMsg = '%s != %s' % (safe_repr(xml1, True), safe_repr(xml2, True))
                diff = ('\n' + '\n'.join(
                    difflib.ndiff(xml1.splitlines(), xml2.splitlines())
                ))
                standardMsg = self._truncateMessage(standardMsg, diff)
                self.fail(self._formatMessage(msg, standardMsg))

    def assertXMLNotEqual(self, xml1, xml2, msg=None):
        """
        Assert that two XML snippets are not semantically equivalent.
        Whitespace in most cases is ignored and attribute ordering is not
        significant. The arguments must be valid XML.
        """
        try:
            result = compare_xml(xml1, xml2)
        except Exception as e:
            standardMsg = 'First or second argument is not valid XML\n%s' % e
            self.fail(self._formatMessage(msg, standardMsg))
        else:
            if result:
                standardMsg = '%s == %s' % (safe_repr(xml1, True), safe_repr(xml2, True))
                self.fail(self._formatMessage(msg, standardMsg))


class TransactionTestCase(SimpleTestCase):

    # Subclasses can ask for resetting of auto increment sequence before each
    # test case
    reset_sequences = False

    # Subclasses can enable only a subset of apps for faster tests
    available_apps = None

    # Subclasses can define fixtures which will be automatically installed.
    fixtures = None

    # Do the tests in this class query non-default databases?
    multi_db = False

    # If transactions aren't available, Django will serialize the database
    # contents into a fixture during setup and flush and reload them
    # during teardown (as flush does not restore data from migrations).
    # This can be slow; this flag allows enabling on a per-case basis.
    serialized_rollback = False

    # Since tests will be wrapped in a transaction, or serialized if they
    # are not available, we allow queries to be run.
    allow_database_queries = True

    def _pre_setup(self):
        """
        Perform pre-test setup:
        * If the class has an 'available_apps' attribute, restrict the app
          registry to these applications, then fire the post_migrate signal --
          it must run with the correct set of applications for the test case.
        * If the class has a 'fixtures' attribute, install those fixtures.
        """
        super()._pre_setup()
        if self.available_apps is not None:
            apps.set_available_apps(self.available_apps)
            setting_changed.send(
                sender=settings._wrapped.__class__,
                setting='INSTALLED_APPS',
                value=self.available_apps,
                enter=True,
            )
            for db_name in self._databases_names(include_mirrors=False):
                emit_post_migrate_signal(verbosity=0, interactive=False, db=db_name)
        try:
            self._fixture_setup()
        except Exception:
            if self.available_apps is not None:
                apps.unset_available_apps()
                setting_changed.send(
                    sender=settings._wrapped.__class__,
                    setting='INSTALLED_APPS',
                    value=settings.INSTALLED_APPS,
                    enter=False,
                )
            raise
        # Clear the queries_log so that it's less likely to overflow (a single
        # test probably won't execute 9K queries). If queries_log overflows,
        # then assertNumQueries() doesn't work.
        for db_name in self._databases_names(include_mirrors=False):
            connections[db_name].queries_log.clear()

    @classmethod
    def _databases_names(cls, include_mirrors=True):
        # If the test case has a multi_db=True flag, act on all databases,
        # including mirrors or not. Otherwise, just on the default DB.
        if cls.multi_db:
            return [
                alias for alias in connections
                if include_mirrors or not connections[alias].settings_dict['TEST']['MIRROR']
            ]
        else:
            return [DEFAULT_DB_ALIAS]

    def _reset_sequences(self, db_name):
        conn = connections[db_name]
        if conn.features.supports_sequence_reset:
            sql_list = conn.ops.sequence_reset_by_name_sql(
                no_style(), conn.introspection.sequence_list())
            if sql_list:
                with transaction.atomic(using=db_name):
                    with conn.cursor() as cursor:
                        for sql in sql_list:
                            cursor.execute(sql)

    def _fixture_setup(self):
        for db_name in self._databases_names(include_mirrors=False):
            # Reset sequences
            if self.reset_sequences:
                self._reset_sequences(db_name)

            # If we need to provide replica initial data from migrated apps,
            # then do so.
            if self.serialized_rollback and hasattr(connections[db_name], "_test_serialized_contents"):
                if self.available_apps is not None:
                    apps.unset_available_apps()
                connections[db_name].creation.deserialize_db_from_string(
                    connections[db_name]._test_serialized_contents
                )
                if self.available_apps is not None:
                    apps.set_available_apps(self.available_apps)

            if self.fixtures:
                # We have to use this slightly awkward syntax due to the fact
                # that we're using *args and **kwargs together.
                call_command('loaddata', *self.fixtures,
                             **{'verbosity': 0, 'database': db_name})

    def _should_reload_connections(self):
        return True

    def _post_teardown(self):
        """
        Perform post-test things:
        * Flush the contents of the database to leave a clean slate. If the
          class has an 'available_apps' attribute, don't fire post_migrate.
        * Force-close the connection so the next test gets a clean cursor.
        """
        try:
            self._fixture_teardown()
            super()._post_teardown()
            if self._should_reload_connections():
                # Some DB cursors include SQL statements as part of cursor
                # creation. If you have a test that does a rollback, the effect
                # of these statements is lost, which can affect the operation of
                # tests (e.g., losing a timezone setting causing objects to be
                # created with the wrong time). To make sure this doesn't
                # happen, get a clean connection at the start of every test.
                for conn in connections.all():
                    conn.close()
        finally:
            if self.available_apps is not None:
                apps.unset_available_apps()
                setting_changed.send(sender=settings._wrapped.__class__,
                                     setting='INSTALLED_APPS',
                                     value=settings.INSTALLED_APPS,
                                     enter=False)

    def _fixture_teardown(self):
        # Allow TRUNCATE ... CASCADE and don't emit the post_migrate signal
        # when flushing only a subset of the apps
        for db_name in self._databases_names(include_mirrors=False):
            # Flush the database
            inhibit_post_migrate = (
                self.available_apps is not None or
                (   # Inhibit the post_migrate signal when using serialized
                    # rollback to avoid trying to recreate the serialized data.
                    self.serialized_rollback and
                    hasattr(connections[db_name], '_test_serialized_contents')
                )
            )
            call_command('flush', verbosity=0, interactive=False,
                         database=db_name, reset_sequences=False,
                         allow_cascade=self.available_apps is not None,
                         inhibit_post_migrate=inhibit_post_migrate)

    def assertQuerysetEqual(self, qs, values, transform=repr, ordered=True, msg=None):
        items = map(transform, qs)
        if not ordered:
            return self.assertEqual(Counter(items), Counter(values), msg=msg)
        values = list(values)
        # For example qs.iterator() could be passed as qs, but it does not
        # have 'ordered' attribute.
        if len(values) > 1 and hasattr(qs, 'ordered') and not qs.ordered:
            raise ValueError("Trying to compare non-ordered queryset "
                             "against more than one ordered values")
        return self.assertEqual(list(items), values, msg=msg)

    def assertNumQueries(self, num, func=None, *args, using=DEFAULT_DB_ALIAS, **kwargs):
        conn = connections[using]

        context = _AssertNumQueriesContext(self, num, conn)
        if func is None:
            return context

        with context:
            func(*args, **kwargs)


def connections_support_transactions():
    """Return True if all connections support transactions."""
    return all(conn.features.supports_transactions for conn in connections.all())


class TestCase(TransactionTestCase):
    """
    Similar to TransactionTestCase, but use `transaction.atomic()` to achieve
    test isolation.

    In most situations, TestCase should be preferred to TransactionTestCase as
    it allows faster execution. However, there are some situations where using
    TransactionTestCase might be necessary (e.g. testing some transactional
    behavior).

    On database backends with no transaction support, TestCase behaves as
    TransactionTestCase.
    """
    @classmethod
    def _enter_atomics(cls):
        """Open atomic blocks for multiple databases."""
        atomics = {}
        for db_name in cls._databases_names():
            atomics[db_name] = transaction.atomic(using=db_name)
            atomics[db_name].__enter__()
        return atomics

    @classmethod
    def _rollback_atomics(cls, atomics):
        """Rollback atomic blocks opened by the previous method."""
        for db_name in reversed(cls._databases_names()):
            transaction.set_rollback(True, using=db_name)
            atomics[db_name].__exit__(None, None, None)

    @classmethod
    def setUpClass(cls):
        super().setUpClass()
        if not connections_support_transactions():
            return
        cls.cls_atomics = cls._enter_atomics()

        if cls.fixtures:
            for db_name in cls._databases_names(include_mirrors=False):
                try:
                    call_command('loaddata', *cls.fixtures, **{'verbosity': 0, 'database': db_name})
                except Exception:
                    cls._rollback_atomics(cls.cls_atomics)
                    raise
        try:
            cls.setUpTestData()
        except Exception:
            cls._rollback_atomics(cls.cls_atomics)
            raise

    @classmethod
    def tearDownClass(cls):
        if connections_support_transactions():
            cls._rollback_atomics(cls.cls_atomics)
            for conn in connections.all():
                conn.close()
        super().tearDownClass()

    @classmethod
    def setUpTestData(cls):
        """Load initial data for the TestCase."""
        pass

    def _should_reload_connections(self):
        if connections_support_transactions():
            return False
        return super()._should_reload_connections()

    def _fixture_setup(self):
        if not connections_support_transactions():
            # If the backend does not support transactions, we should reload
            # class data before each test
            self.setUpTestData()
            return super()._fixture_setup()

        assert not self.reset_sequences, 'reset_sequences cannot be used on TestCase instances'
        self.atomics = self._enter_atomics()

    def _fixture_teardown(self):
        if not connections_support_transactions():
            return super()._fixture_teardown()
        try:
            for db_name in reversed(self._databases_names()):
                if self._should_check_constraints(connections[db_name]):
                    connections[db_name].check_constraints()
        finally:
            self._rollback_atomics(self.atomics)

    def _should_check_constraints(self, connection):
        return (
            connection.features.can_defer_constraint_checks and
            not connection.needs_rollback and connection.is_usable()
        )


class CheckCondition:
    """Descriptor class for deferred condition checking."""
    def __init__(self, *conditions):
        self.conditions = conditions

    def add_condition(self, condition, reason):
        return self.__class__(*self.conditions, (condition, reason))

    def __get__(self, instance, cls=None):
        # Trigger access for all bases.
        if any(getattr(base, '__unittest_skip__', False) for base in cls.__bases__):
            return True
        for condition, reason in self.conditions:
            if condition():
                # Override this descriptor's value and set the skip reason.
                cls.__unittest_skip__ = True
                cls.__unittest_skip_why__ = reason
                return True
        return False


def _deferredSkip(condition, reason):
    def decorator(test_func):
        if not (isinstance(test_func, type) and
                issubclass(test_func, unittest.TestCase)):
            @wraps(test_func)
            def skip_wrapper(*args, **kwargs):
                if condition():
                    raise unittest.SkipTest(reason)
                return test_func(*args, **kwargs)
            test_item = skip_wrapper
        else:
            # Assume a class is decorated
            test_item = test_func
            # Retrieve the possibly existing value from the class's dict to
            # avoid triggering the descriptor.
            skip = test_func.__dict__.get('__unittest_skip__')
            if isinstance(skip, CheckCondition):
                test_item.__unittest_skip__ = skip.add_condition(condition, reason)
            elif skip is not True:
                test_item.__unittest_skip__ = CheckCondition((condition, reason))
        return test_item
    return decorator


def skipIfDBFeature(*features):
    """Skip a test if a database has at least one of the named features."""
    return _deferredSkip(
        lambda: any(getattr(connection.features, feature, False) for feature in features),
        "Database has feature(s) %s" % ", ".join(features)
    )


def skipUnlessDBFeature(*features):
    """Skip a test unless a database has all the named features."""
    return _deferredSkip(
        lambda: not all(getattr(connection.features, feature, False) for feature in features),
        "Database doesn't support feature(s): %s" % ", ".join(features)
    )


def skipUnlessAnyDBFeature(*features):
    """Skip a test unless a database has any of the named features."""
    return _deferredSkip(
        lambda: not any(getattr(connection.features, feature, False) for feature in features),
        "Database doesn't support any of the feature(s): %s" % ", ".join(features)
    )


class QuietWSGIRequestHandler(WSGIRequestHandler):
    """
    A WSGIRequestHandler that doesn't log to standard output any of the
    requests received, so as to not clutter the test result output.
    """
    def log_message(*args):
        pass


class FSFilesHandler(WSGIHandler):
    """
    WSGI middleware that intercepts calls to a directory, as defined by one of
    the *_ROOT settings, and serves those files, publishing them under *_URL.
    """
    def __init__(self, application):
        self.application = application
        self.base_url = urlparse(self.get_base_url())
        super().__init__()

    def _should_handle(self, path):
        """
        Check if the path should be handled. Ignore the path if:
        * the host is provided as part of the base_url
        * the request's path isn't under the media path (or equal)
        """
        return path.startswith(self.base_url[2]) and not self.base_url[1]

    def file_path(self, url):
        """Return the relative path to the file on disk for the given URL."""
        relative_url = url[len(self.base_url[2]):]
        return url2pathname(relative_url)

    def get_response(self, request):
        from django.http import Http404

        if self._should_handle(request.path):
            try:
                return self.serve(request)
            except Http404:
                pass
        return super().get_response(request)

    def serve(self, request):
        os_rel_path = self.file_path(request.path)
        os_rel_path = posixpath.normpath(unquote(os_rel_path))
        # Emulate behavior of django.contrib.staticfiles.views.serve() when it
        # invokes staticfiles' finders functionality.
        # TODO: Modify if/when that internal API is refactored
        final_rel_path = os_rel_path.replace('\\', '/').lstrip('/')
        return serve(request, final_rel_path, document_root=self.get_base_dir())

    def __call__(self, environ, start_response):
        if not self._should_handle(get_path_info(environ)):
            return self.application(environ, start_response)
        return super().__call__(environ, start_response)


class _StaticFilesHandler(FSFilesHandler):
    """
    Handler for serving static files. A private class that is meant to be used
    solely as a convenience by LiveServerThread.
    """
    def get_base_dir(self):
        return settings.STATIC_ROOT

    def get_base_url(self):
        return settings.STATIC_URL


class _MediaFilesHandler(FSFilesHandler):
    """
    Handler for serving the media files. A private class that is meant to be
    used solely as a convenience by LiveServerThread.
    """
    def get_base_dir(self):
        return settings.MEDIA_ROOT

    def get_base_url(self):
        return settings.MEDIA_URL


class LiveServerThread(threading.Thread):
    """Thread for running a live http server while the tests are running."""

    def __init__(self, host, static_handler, connections_override=None, port=0):
        self.host = host
        self.port = port
        self.is_ready = threading.Event()
        self.error = None
        self.static_handler = static_handler
        self.connections_override = connections_override
        super().__init__()

    def run(self):
        """
        Set up the live server and databases, and then loop over handling
        HTTP requests.
        """
        if self.connections_override:
            # Override this thread's database connections with the ones
            # provided by the main thread.
            for alias, conn in self.connections_override.items():
                connections[alias] = conn
        try:
            # Create the handler for serving static and media files
            handler = self.static_handler(_MediaFilesHandler(WSGIHandler()))
            self.httpd = self._create_server()
            # If binding to port zero, assign the port allocated by the OS.
            if self.port == 0:
                self.port = self.httpd.server_address[1]
            self.httpd.set_app(handler)
            self.is_ready.set()
            self.httpd.serve_forever()
        except Exception as e:
            self.error = e
            self.is_ready.set()
        finally:
            connections.close_all()

    def _create_server(self):
        return ThreadedWSGIServer((self.host, self.port), QuietWSGIRequestHandler, allow_reuse_address=False)

    def terminate(self):
        if hasattr(self, 'httpd'):
            # Stop the WSGI server
            self.httpd.shutdown()
            self.httpd.server_close()
        self.join()


class LiveServerTestCase(TransactionTestCase):
    """
    Do basically the same as TransactionTestCase but also launch a live HTTP
    server in a separate thread so that the tests may use another testing
    framework, such as Selenium for example, instead of the built-in dummy
    client.
    It inherits from TransactionTestCase instead of TestCase because the
    threads don't share the same transactions (unless if using in-memory sqlite)
    and each thread needs to commit all their transactions so that the other
    thread can see the changes.
    """
    host = 'localhost'
    port = 0
    server_thread_class = LiveServerThread
    static_handler = _StaticFilesHandler

    @classproperty
    def live_server_url(cls):
        return 'http://%s:%s' % (cls.host, cls.server_thread.port)

    @classmethod
    def setUpClass(cls):
        super().setUpClass()
        connections_override = {}
        for conn in connections.all():
            # If using in-memory sqlite databases, pass the connections to
            # the server thread.
            if conn.vendor == 'sqlite' and conn.is_in_memory_db():
                # Explicitly enable thread-shareability for this connection
                conn.allow_thread_sharing = True
                connections_override[conn.alias] = conn

        cls._live_server_modified_settings = modify_settings(
            ALLOWED_HOSTS={'append': cls.host},
        )
        cls._live_server_modified_settings.enable()
        cls.server_thread = cls._create_server_thread(connections_override)
        cls.server_thread.daemon = True
        cls.server_thread.start()

        # Wait for the live server to be ready
        cls.server_thread.is_ready.wait()
        if cls.server_thread.error:
            # Clean up behind ourselves, since tearDownClass won't get called in
            # case of errors.
            cls._tearDownClassInternal()
            raise cls.server_thread.error

    @classmethod
    def _create_server_thread(cls, connections_override):
        return cls.server_thread_class(
            cls.host,
            cls.static_handler,
            connections_override=connections_override,
            port=cls.port,
        )

    @classmethod
    def _tearDownClassInternal(cls):
        # There may not be a 'server_thread' attribute if setUpClass() for some
        # reasons has raised an exception.
        if hasattr(cls, 'server_thread'):
            # Terminate the live server's thread
            cls.server_thread.terminate()

        # Restore sqlite in-memory database connections' non-shareability
        for conn in connections.all():
            if conn.vendor == 'sqlite' and conn.is_in_memory_db():
                conn.allow_thread_sharing = False

    @classmethod
    def tearDownClass(cls):
        cls._tearDownClassInternal()
        cls._live_server_modified_settings.disable()
        super().tearDownClass()


class SerializeMixin:
    """
    Enforce serialization of TestCases that share a common resource.

    Define a common 'lockfile' for each set of TestCases to serialize. This
    file must exist on the filesystem.

    Place it early in the MRO in order to isolate setUpClass()/tearDownClass().
    """
    lockfile = None

    @classmethod
    def setUpClass(cls):
        if cls.lockfile is None:
            raise ValueError(
                "{}.lockfile isn't set. Set it to a unique value "
                "in the base class.".format(cls.__name__))
        cls._lockfile = open(cls.lockfile)
        locks.lock(cls._lockfile, locks.LOCK_EX)
        super().setUpClass()

    @classmethod
    def tearDownClass(cls):
        super().tearDownClass()
        cls._lockfile.close()