input: Write a function to generate an HTML table displaying information about the top 10 bestselling books in a specific genre from a SQLite database. The function should connect to a database, retrieve the data based on the specified genre, and return the generated HTML table as a string.
  assert generate_top_books_table("Fantasy")=="<table><tr><th>Title</th><th>Author</th><th>Genre</th><th>Sales</th></tr><tr><td>Title1</td><td>Author1</td><td>Fantasy</td><td>1000</td></tr><tr><td>Title2</td><td>Author2</td><td>Fantasy</td><td>900</td></tr><tr><td>Title3</td><td>Author3</td><td>Fantasy</td><td>800</td></tr><tr><td>Title4</td><td>Author4</td><td>Fantasy</td><td>700</td></tr><tr><td>Title5</td><td>Author5</td><td>Fantasy</td><td>600</td></tr></table>"
  assert generate_top_books_table("Sci-Fi")=="<table><tr><th>Title</th><th>Author</th><th>Genre</th><th>Sales</th></tr><tr><td>Title1</td><td>Author1</td><td>Sci-Fi</td><td>1200</td></tr><tr><td>Title2</td><td>Author2</td><td>Sci-Fi</td><td>1100</td></tr><tr><td>Title3</td><td>Author3</td><td>Sci-Fi</td><td>1000</td></tr><tr><td>Title4</td><td>Author4</td><td>Sci-Fi</td><td>900</td></tr><tr><td>Title5</td><td>Author5</td><td>Sci-Fi</td><td>800</td></tr></table>"
output: 
  def generate_top_books_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()
      
      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
  