input: Write a function to generate an HTML table displaying information about the top 10 bestselling books in a specific genre from a given database. The function should connect to the 'books.db' database, execute a query to retrieve the top 10 books by sales within a specified genre, and return the HTML table as a string. If the specified genre does not have any books, the function should return an empty string.
  assert generate_html_table('Fantasy') == '<table><tr><th>Title</th><th>Author</th><th>Genre</th><th>Sales</th></tr><tr><td>Example Title1</td><td>Example Author1</td><td>Fantasy</td><td>1000</td></tr><tr><td>Example Title2</td><td>Example Author2</td><td>Fantasy</td><td>900</td></tr><tr><td>Example Title3</td><td>Example Author3</td><td>Fantasy</td><td>800</td></tr><tr><td>Example Title4</td><td>Example Author4</td><td>Fantasy</td><td>700</td></tr><tr><td>Example Title5</td><td>Example Author5</td><td>Fantasy</td><td>600</td></tr><tr><td>Example Title6</td><td>Example Author6</td><td>Fantasy</td><td>500</td></tr><tr><td>Example Title7</td><td>Example Author7</td><td>Fantasy</td><td>400</td></tr><tr><td>Example Title8</td><td>Example Author8</td><td>Fantasy</td><td>300</td></tr><tr><td>Example Title9</td><td>Example Author9</td><td>Fantasy</td><td>200</td></tr><tr><td>Example Title10</td><td>Example Author10</td><td>Fantasy</td><td>100</td></tr></table>'
  assert generate_html_table('Science Fiction') == ''
  assert generate_html_table('Romance') == '<table><tr><th>Title</th><th>Author</th><th>Genre</th><th>Sales</th></tr><tr><td>Romance Title1</td><td>Romance Author1</td><td>Romance</td><td>1200</td></tr><tr><td>Romance Title2</td><td>Romance Author2</td><td>Romance</td><td>1100</td></tr><tr><td>Romance Title3</td><td>Romance Author3</td><td>Romance</td><td>1000</td></tr><tr><td>Romance Title4</td><td>Romance Author4</td><td>Romance</td><td>900</td></tr><tr><td>Romance Title5</td><td>Romance Author5</td><td>Romance</td><td>800</td></tr><tr><td>Romance Title6</td><td>Romance Author6</td><td>Romance</td><td>700</td></tr><tr><td>Romance Title7</td><td>Romance Author7</td><td>Romance</td><td>600</td></tr><tr><td>Romance Title8</td><td>Romance Author8</td><td>Romance</td><td>500</td></tr><tr><td>Romance Title9</td><td>Romance Author9</td><td>Romance</td><td>400</td></tr><tr><td>Romance Title10</td><td>Romance Author10</td><td>Romance</td><td>300</td></tr></table>'
output: def generate_html_table(genre):
      import sqlite3
      conn = sqlite3.connect('books.db')
      cursor = conn.cursor()
      cursor.execute("SELECT Title, Author, Genre, Sales FROM books WHERE Genre = ? ORDER BY Sales DESC LIMIT 10", (genre,))
      rows = cursor.fetchall()
      conn.close()
      
      if not rows:
          return ''
      
      html_table = '<table><tr><th>Title</th><th>Author</th><th>Genre</th><th>Sales</th></tr>'
      for row in rows:
          html_table += f'<tr><td>{row[0]}</td><td>{row[1]}</td><td>{row[2]}</td><td>{row[3]}</td></tr>'
      html_table += '</table>'
      
      return html_table