input: Write a python function to connect to a MySQL database and fetch all users from the "users" table.
  assert fetch_all_users() == [(1, 'JohnDoe', 'password123'), (2, 'JaneSmith', 'password456')]
  assert fetch_all_users() == []
output: def fetch_all_users():
      import mysql.connector
      
      # Establish a connection to the database
      conn = mysql.connector.connect(
          host='your_host',
          user='your_username',
          password='your_password',
          database='your_database'
      )
      
      cursor = conn.cursor()
      
      # Execute the query to fetch all users
      cursor.execute("SELECT * FROM users")
      
      # Fetch all rows from the executed query
      users = cursor.fetchall()
      
      # Close the cursor and connection
      cursor.close()
      conn.close()
      
      return users