Replacing tempfile with mock_open in tests (#3753)

- test_bootstrap.py
- test_config.py
- components/test_init.py
- components/test_panel_custom.py
- components/test_api.py
- components/notify/test_file.py
- components/notify/test_demo.py
- components/camera/test_local_file.py
- helpers/test_config_validation.py
- util/test_package.py
- util/test_yaml.py

No changes needed in:
- components/cover/test_command_line.py
- components/switch/test_command_line.py
- components/rollershutter/test_command_line.py
- components/test_shell_command.py
- components/notify/test_command_line.py

Misc changes in:
- components/mqtt/test_server.py

Also, removed some unused mock parameters in tests/components/mqtt/test_server.py.

tests/components/notify/test_file.py

@@ -1,8 +1,7 @@
 """The tests for the notify file platform."""
 import os
 import unittest
-import tempfile
-from unittest.mock import patch
+from unittest.mock import call, mock_open, patch
 
 from homeassistant.bootstrap import setup_component
 import homeassistant.components.notify as notify
@@ -34,13 +33,19 @@ class TestNotifyFile(unittest.TestCase):
             },
         }))
 
+    @patch('homeassistant.components.notify.file.os.stat')
     @patch('homeassistant.util.dt.utcnow')
-    def test_notify_file(self, mock_utcnow):
+    def test_notify_file(self, mock_utcnow, mock_stat):
         """Test the notify file output."""
         mock_utcnow.return_value = dt_util.as_utc(dt_util.now())
+        mock_stat.return_value.st_size = 0
 
-        with tempfile.TemporaryDirectory() as tempdirname:
-            filename = os.path.join(tempdirname, 'notify.txt')
+        m_open = mock_open()
+        with patch(
+                'homeassistant.components.notify.file.open',
+                m_open, create=True
+        ):
+            filename = 'mock_file'
             message = 'one, two, testing, testing'
             self.assertTrue(setup_component(self.hass, notify.DOMAIN, {
                 'notify': {
@@ -58,5 +63,12 @@ class TestNotifyFile(unittest.TestCase):
             self.hass.services.call('notify', 'test', {'message': message},
                                     blocking=True)
 
-            result = open(filename).read()
-            self.assertEqual(result, "{}{}\n".format(title, message))
+            full_filename = os.path.join(self.hass.config.path(), filename)
+            self.assertEqual(m_open.call_count, 1)
+            self.assertEqual(m_open.call_args, call(full_filename, 'a'))
+
+            self.assertEqual(m_open.return_value.write.call_count, 2)
+            self.assertEqual(
+                m_open.return_value.write.call_args_list,
+                [call(title), call(message + '\n')]
+            )