input: Write a function to convert a given SQL statement into a Python Pandas DataFrame. The function should take a SQL query string and a database connection object as parameters, execute the query, and return the resulting DataFrame.
  
  def sql_to_df(sql_query, conn):
      import pandas as pd
      return pd.read_sql_query(sql_query, conn)
  
  assert sql_to_df("SELECT * FROM book;", conn).equals(pd.DataFrame([[1, 'Title1', 'Author1'], [2, 'Title2', 'Author2']], columns=['id', 'title', 'author'])) == True
  assert sql_to_df("SELECT * FROM author;", conn).equals(pd.DataFrame([['Author1'], ['Author2']], columns=['author'])) == True
  assert sql_to_df("SELECT * FROM empty_table;", conn).empty == True
  assert sql_to_df("SELECT * FROM book WHERE id > 3;", conn).empty == True
output: def sql_to_df(sql_query, conn):
      import pandas as pd
      return pd.read_sql_query(sql_query, conn)