input: Write a function to create a web crawler in Python that starts from a website and looks for other links in the page then scrapes the page content. Use the following function header: `def crawl(url)`. Implement a mechanism to track visited URLs and use a queue to manage URLs that need to be processed. Assert the following test cases:
  
  assert crawl("http://example.com") # Assuming it scrapes the content and finds links as expected.
  assert crawl("http://anotherexample.com") # Assuming it scrapes the content and finds links as expected.
  assert crawl("http://nonexistentdomain.com") # Assuming it handles the case where the domain does not exist.
output: def crawl(url):
      import requests
      from bs4 import BeautifulSoup
      from urllib.parse import urljoin
      from collections import deque
  
      visited = set()
      queue = deque([url])
  
      while queue:
          current_url = queue.popleft()
          if current_url in visited:
              continue
          visited.add(current_url)
  
          try:
              response = requests.get(current_url)
              if response.status_code != 200:
                  continue
          except requests.RequestException:
              continue
  
          soup = BeautifulSoup(response.text, 'html.parser')
          # Scrape content here if needed
  
          for link in soup.find_all('a', href=True):
              absolute_url = urljoin(current_url, link['href'])
              if absolute_url not in visited:
                  queue.append(absolute_url)