A website should have one canonical URL for the homepage (https://www.example.com). The other URLs should redirect there.
This test will check all four versions of the homepage (with and without SSL, with and without 'www') and check to make sure that one of them is canonical and the others redirect there. This is important for SEO reasons. Search engines can see 'example.com' and 'www.example.com' as being two separate websites, so you should select one and have the other redirect. Whether you use the 'www' or not is a matter of taste. Additionally, if you serve content over SSL (which you should), the server should redirect all 'http' urls to 'https'.
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