Issue #21750: Further fixup to be styled like other mock APIs.

Lib/unittest/test/testmock/testmock.py

@@ -1,5 +1,6 @@
 import copy
 import sys
+import tempfile
 
 import unittest
 from unittest.test.testmock.support import is_instance
@@ -1374,8 +1375,29 @@ class MockTest(unittest.TestCase):
     def test_mock_open_reuse_issue_21750(self):
         mocked_open = mock.mock_open(read_data='data')
         f1 = mocked_open('a-name')
+        f1_data = f1.read()
         f2 = mocked_open('another-name')
-        self.assertEqual(f1.read(), f2.read())
+        f2_data = f2.read()
+        self.assertEqual(f1_data, f2_data)
+
+    def test_mock_open_write(self):
+        # Test exception in file writing write()
+        mock_namedtemp = mock.mock_open(mock.MagicMock(name='JLV'))
+        with mock.patch('tempfile.NamedTemporaryFile', mock_namedtemp):
+            mock_filehandle = mock_namedtemp.return_value
+            mock_write = mock_filehandle.write
+            mock_write.side_effect = OSError('Test 2 Error')
+            def attempt():
+                tempfile.NamedTemporaryFile().write('asd')
+            self.assertRaises(OSError, attempt)
+
+    def test_mock_open_alter_readline(self):
+        mopen = mock.mock_open(read_data='foo\nbarn')
+        mopen.return_value.readline.side_effect = lambda *args:'abc'
+        first = mopen().readline()
+        second = mopen().readline()
+        self.assertEqual('abc', first)
+        self.assertEqual('abc', second)
 
     def test_mock_parents(self):
         for Klass in Mock, MagicMock: