Use built-in Python 3 unittest.mock module

Replace the use of external 'mock' package with the 'unittest.mock'
module provided by Python 3.  Since Python 2 is no longer supported,
this eliminates an unnecessary dependency.

Author: mgorny

tests/test_integration_distutils.py

@@ -1,6 +1,6 @@
 import distutils.dist
+import unittest.mock
 
-import mock
 import pytest
 import setuptools.dist
 
@@ -11,7 +11,7 @@ def test_valid_rst():
     dist = distutils.dist.Distribution(attrs=dict(
         long_description="Hello, I am some text."))
     checker = readme_renderer.integration.distutils.Check(dist)
-    checker.warn = mock.Mock()
+    checker.warn = unittest.mock.Mock()
 
     checker.check_restructuredtext()
 
@@ -22,14 +22,14 @@ def test_invalid_rst():
     dist = distutils.dist.Distribution(attrs=dict(
         long_description="Hello, I am some `totally borked< text."))
     checker = readme_renderer.integration.distutils.Check(dist)
-    checker.warn = mock.Mock()
-    checker.announce = mock.Mock()
+    checker.warn = unittest.mock.Mock()
+    checker.announce = unittest.mock.Mock()
 
     checker.check_restructuredtext()
 
     # Should warn once for the syntax error, and finally to warn that the
     # overall syntax is invalid
-    checker.warn.assert_called_once_with(mock.ANY)
+    checker.warn.assert_called_once_with(unittest.mock.ANY)
     message = checker.warn.call_args[0][0]
     assert 'invalid markup' in message
     assert 'line 1: Warning:' in message
@@ -47,14 +47,14 @@ def test_malicious_rst():
     dist = distutils.dist.Distribution(attrs=dict(
         long_description=description))
     checker = readme_renderer.integration.distutils.Check(dist)
-    checker.warn = mock.Mock()
-    checker.announce = mock.Mock()
+    checker.warn = unittest.mock.Mock()
+    checker.announce = unittest.mock.Mock()
 
     checker.check_restructuredtext()
 
     # Should warn once for the syntax error, and finally to warn that the
     # overall syntax is invalid
-    checker.warn.assert_called_once_with(mock.ANY)
+    checker.warn.assert_called_once_with(unittest.mock.ANY)
     message = checker.warn.call_args[0][0]
     assert 'directive disabled' in message
 
@@ -68,7 +68,7 @@ def test_markdown():
         long_description="Hello, I am some text.",
         long_description_content_type="text/markdown"))
     checker = readme_renderer.integration.distutils.Check(dist)
-    checker.warn = mock.Mock()
+    checker.warn = unittest.mock.Mock()
 
     checker.check_restructuredtext()
 
@@ -79,21 +79,21 @@ def test_markdown():
 def test_invalid_missing():
     dist = distutils.dist.Distribution(attrs=dict())
     checker = readme_renderer.integration.distutils.Check(dist)
-    checker.warn = mock.Mock()
+    checker.warn = unittest.mock.Mock()
 
     checker.check_restructuredtext()
 
-    checker.warn.assert_called_once_with(mock.ANY)
+    checker.warn.assert_called_once_with(unittest.mock.ANY)
     assert 'missing' in checker.warn.call_args[0][0]
 
 
 def test_invalid_empty():
     dist = distutils.dist.Distribution(attrs=dict(
         long_description=""))
     checker = readme_renderer.integration.distutils.Check(dist)
-    checker.warn = mock.Mock()
+    checker.warn = unittest.mock.Mock()
 
     checker.check_restructuredtext()
 
-    checker.warn.assert_called_once_with(mock.ANY)
+    checker.warn.assert_called_once_with(unittest.mock.ANY)
     assert 'missing' in checker.warn.call_args[0][0]

tox.ini

@@ -4,7 +4,6 @@ envlist = py36,py37,py38,py39,pep8,packaging,noextra
 [testenv]
 deps =
     pytest
-    mock
 commands =
     py.test --strict {posargs}
 extras = md