old_contents: """The tests for the folder sensor."""
  import os
  import unittest
  
  from homeassistant.components.folder.sensor import CONF_FOLDER_PATHS
  from homeassistant.setup import setup_component
  
  from tests.common import get_test_home_assistant
  
  CWD = os.path.join(os.path.dirname(__file__))
  TEST_FOLDER = "test_folder"
  TEST_DIR = os.path.join(CWD, TEST_FOLDER)
  TEST_TXT = "mock_test_folder.txt"
  TEST_FILE = os.path.join(TEST_DIR, TEST_TXT)
  
  
  def create_file(path):
      """Create a test file."""
      with open(path, "w") as test_file:
          test_file.write("test")
  
  
  class TestFolderSensor(unittest.TestCase):
      """Test the filesize sensor."""
  
      def setup_method(self, method):
          """Set up things to be run when tests are started."""
          self.hass = get_test_home_assistant()
          if not os.path.isdir(TEST_DIR):
              os.mkdir(TEST_DIR)
          self.hass.config.allowlist_external_dirs = {TEST_DIR}
  
      def teardown_method(self, method):
          """Stop everything that was started."""
          if os.path.isfile(TEST_FILE):
              os.remove(TEST_FILE)
              os.rmdir(TEST_DIR)
          self.hass.stop()
  
      def test_invalid_path(self):
          """Test that an invalid path is caught."""
          config = {"sensor": {"platform": "folder", CONF_FOLDER_PATHS: "invalid_path"}}
          assert setup_component(self.hass, "sensor", config)
          assert len(self.hass.states.entity_ids()) == 0
  
      def test_valid_path(self):
          """Test for a valid path."""
          create_file(TEST_FILE)
          config = {"sensor": {"platform": "folder", CONF_FOLDER_PATHS: TEST_DIR}}
          assert setup_component(self.hass, "sensor", config)
          self.hass.block_till_done()
          assert len(self.hass.states.entity_ids()) == 1
          state = self.hass.states.get("sensor.test_folder")
          assert state.state == "0.0"
          assert state.attributes.get("number_of_files") == 1
  
new_contents: """The tests for the folder sensor."""
  import os
  
  from homeassistant.components.folder.sensor import CONF_FOLDER_PATHS
  from homeassistant.setup import async_setup_component
  
  CWD = os.path.join(os.path.dirname(__file__))
  TEST_FOLDER = "test_folder"
  TEST_DIR = os.path.join(CWD, TEST_FOLDER)
  TEST_TXT = "mock_test_folder.txt"
  TEST_FILE = os.path.join(TEST_DIR, TEST_TXT)
  
  
  def create_file(path):
      """Create a test file."""
      with open(path, "w") as test_file:
          test_file.write("test")
  
  
  def remove_test_file():
      """Remove test file."""
      if os.path.isfile(TEST_FILE):
          os.remove(TEST_FILE)
          os.rmdir(TEST_DIR)
  
  
  async def test_invalid_path(hass):
      """Test that an invalid path is caught."""
      config = {"sensor": {"platform": "folder", CONF_FOLDER_PATHS: "invalid_path"}}
      assert await async_setup_component(hass, "sensor", config)
      assert len(hass.states.async_entity_ids()) == 0
  
  
  async def test_valid_path(hass):
      """Test for a valid path."""
      if not os.path.isdir(TEST_DIR):
          os.mkdir(TEST_DIR)
      create_file(TEST_FILE)
  
      hass.config.allowlist_external_dirs = {TEST_DIR}
      config = {"sensor": {"platform": "folder", CONF_FOLDER_PATHS: TEST_DIR}}
      assert await async_setup_component(hass, "sensor", config)
      await hass.async_block_till_done()
      assert len(hass.states.async_entity_ids()) == 1
      state = hass.states.get("sensor.test_folder")
      assert state.state == "0.0"
      assert state.attributes.get("number_of_files") == 1
  
      remove_test_file()
  
subject: Rewrite folder unittest tests to pytest style test functions (#41672)