input: Write a python function to scrape stock data from the Wall Street Journal website.
  assert 'AAPL' in scrape_stock_data()
  assert 'GOOGL' in scrape_stock_data()
  assert 'MSFT' in scrape_stock_data()
output: def scrape_stock_data():
      import requests
      from bs4 import BeautifulSoup
  
      url = "https://www.wsj.com/market-data/stocks"
      response = requests.get(url)
      soup = BeautifulSoup(response.text, 'html.parser')
  
      stock_symbols = set()
      for a in soup.find_all('a', class_='WSJTheme--link'):
          if a.text.isupper() and len(a.text) <= 5:  # crude filter for stock symbols
              stock_symbols.add(a.text)
      
      return stock_symbols