Use assert(mock.called) (#33194)

The `mock.assert_called()` method was added in Python 3.6,
so fails on some of our older CI machines that use Python 3.5.
`assert(mock.called)` is precisely equivalent and works with
older versions of the Python unittest.mock library.

Author: tbkka

utils/build_swift/tests/build_swift/test_cache_utils.py

@@ -49,7 +49,7 @@ def test_replaced_with_functools_lru_cache_python_3_2(self):
             def func():
                 return None
 
-        mock_lru_cache.assert_called()
+        assert(mock_lru_cache.called)
 
     def test_call_with_no_args(self):
         # Increments the counter once per unique call.

utils/build_swift/tests/build_swift/test_shell.py

@@ -118,7 +118,7 @@ def test_echo_command(self):
 
         mock_stream.write.assert_called_with(
             '>>> {}\n'.format(shell.quote(test_command)))
-        mock_stream.flush.assert_called()
+        assert(mock_stream.flush.called)
 
     @utils.requires_module('unittest.mock')
     def test_echo_command_custom_prefix(self):
@@ -127,7 +127,7 @@ def test_echo_command_custom_prefix(self):
         shell._echo_command('ls', mock_stream, prefix='$ ')
 
         mock_stream.write.assert_called_with('$ ls\n')
-        mock_stream.flush.assert_called()
+        assert(mock_stream.flush.called)
 
     # -------------------------------------------------------------------------
     # _normalize_args
@@ -208,8 +208,8 @@ def func(command, **kwargs):
             self.assertEqual(kwargs['stdout'], mock_file)
 
         func('', stdout=shell.DEVNULL)
-        mock_open.return_value.__enter__.assert_called()
-        mock_open.return_value.__exit__.assert_called()
+        assert(mock_open.return_value.__enter__.called)
+        assert(mock_open.return_value.__exit__.called)
 
     @utils.requires_module('unittest.mock')
     @patch(_OPEN_NAME, new_callable=mock_open)
@@ -223,8 +223,8 @@ def func(command, **kwargs):
             self.assertEqual(kwargs['stderr'], mock_file)
 
         func('', stderr=shell.DEVNULL)
-        mock_open.return_value.__enter__.assert_called()
-        mock_open.return_value.__exit__.assert_called()
+        assert(mock_open.return_value.__enter__.called)
+        assert(mock_open.return_value.__exit__.called)
 
     @utils.requires_module('unittest.mock')
     @patch(_OPEN_NAME, new_callable=mock_open)