input: Write a function to extract headlines using Scrapy framework.
  assert extract_headlines('http://www.bbc.com/news')==['Headline 1', 'Headline 2', 'Headline 3']
  assert extract_headlines('http://www.bbc.com/news/world')==['World Headline 1', 'World Headline 2']
  assert extract_headlines('http://www.bbc.com/news/technology')==['Tech Headline 1', 'Tech Headline 2']
output: def extract_headlines(url):
      import scrapy
      from scrapy.crawler import CrawlerProcess
      
      class HeadlineSpider(scrapy.Spider):
          name = "headline_spider"
          start_urls = [url]
          
          def parse(self, response):
              headlines = response.css('h3::text').getall()
              self.headlines = headlines
              
      process = CrawlerProcess(settings={
          "LOG_LEVEL": "ERROR",
      })
      
      spider = HeadlineSpider()
      process.crawl(spider)
      process.start()
      
      return spider.headlines