Google recently notified via a blog post that they are going to provide more accurate crawl errors under Google Webmasters Tools. Earlier if any crawl error URL, A redirected to URL B, Google would have displayed URL A under error report but now the crawl error would be identified to B as A is getting redirected to B.
The crawl error section in Google displays a list of URL's that Google is unable to crawl. You can view the crawl errors by following the below steps:
There are 2 main types of crawl errors:
Site Errors - Normally happens when Google is unable to crawl the website because of restricted robots.txt.
URL Errors - This type of error is shown when Google can't crawl specific URL's because.
See full list of crawl errors.
The best way to check if all your URL's are working is by making use of Fetch as Googlebot tool.