refactor: switch from mock to unittest.mock (#34844)

As of Python 3.3, the 3rd-party `mock` package has been subsumed into the
standard `unittest.mock` package. Refactoring tests to use the latter will
allow us to drop `mock` as a dependency, which is currently coming in
transitively through requirements/edx/paver.in.

We don't actually drop the `mock` dependency in this PR. That will happen
naturally in:

* https://github.com/openedx/edx-platform/pull/34830

xmodule/capa/tests/helpers.py

@@ -6,10 +6,10 @@ import io
 import os
 import os.path
 import xml.sax.saxutils as saxutils
+from unittest.mock import MagicMock, Mock
 
 import fs.osfs
 from mako.lookup import TemplateLookup
-from mock import MagicMock, Mock
 from path import Path
 
 from xmodule.capa.capa_problem import LoncapaProblem, LoncapaSystem

xmodule/capa/tests/test_capa_problem.py

@@ -3,6 +3,7 @@ Test capa problem.
 """
 import textwrap
 import unittest
+from unittest.mock import patch, MagicMock
 
 from django.conf import settings
 from django.test import override_settings
@@ -10,7 +11,6 @@ import pytest
 import ddt
 from lxml import etree
 from markupsafe import Markup
-from mock import patch, MagicMock
 
 from xmodule.capa.correctmap import CorrectMap
 from xmodule.capa.responsetypes import LoncapaProblemError

xmodule/capa/tests/test_html_render.py

@@ -6,9 +6,9 @@ CAPA HTML rendering tests.
 import os
 import textwrap
 import unittest
+from unittest import mock
 
 import ddt
-import mock
 from lxml import etree
 from xmodule.capa.tests.helpers import new_loncapa_problem, test_capa_system
 from openedx.core.djangolib.markup import HTML

xmodule/capa/tests/test_inputtypes.py

@@ -23,12 +23,12 @@ import textwrap
 import unittest
 import xml.sax.saxutils as saxutils
 from collections import OrderedDict
+from unittest.mock import ANY, patch
 
 import pytest
 import six
 from lxml import etree
 from lxml.html import fromstring
-from mock import ANY, patch
 from pyparsing import ParseException
 from six.moves import zip
 

xmodule/capa/tests/test_responsetypes.py

@@ -9,10 +9,10 @@ import textwrap
 import unittest
 import zipfile
 from datetime import datetime
+from unittest import mock
 
 import pytest
 import calc
-import mock
 import pyparsing
 import random2 as random
 import requests