Tests that there is at most one redirect when accessing the website.
The homepage of a website can be accessed in 4 different ways. With and without the 'www' prefix and with and without SSL.
Best practices are to pick one of the last two options and have the other three permanently redirect to that place. This is important for SEO purposes as it tells search engines that there is one canonical URL for the homepage and that any links pointing to any of these four URLs all refer to the same page.
A redirect chain is when there is more than one redirect to the final destination. A common error is that a user types "example.com" into their web browser. This loads "http://example.com" and then the server upgrades the connection to SSL and redirects to "https://example.com". The browser then fetches this new page which adds the 'www' prefix and performs another redirect to "https://www.example.com". These multiple redirects make the page load slower for the user. The solution in this case would be to fix the original redirect to add the 'www' and the 'https' at the same time.
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