I looked into it and made a little improvement (will create pull request shortly).

The logs for this set of URLs:

<urls>      
    <url href=""/>
    <url href="/test0"/>
    <url href="/test0"/>
    <url href="/test1" name="name-1"/>
    <url href="/test1" name="name-1"/>
    <url href="/test2" name="name-2"/>
    <url href="/test2" name="name-3"/>
    <url href="/test3" description="description-1"/>
    <url href="/test3" description="description-1"/>
    <url href="/test4" description="description-2"/>
    <url href="/test4" description="description-3"/>
</urls>

Will be:

[Status: 400] Something is wrong with your suite definition! Detected errors: 
Empty url
Duplicated url, with URL: /test0, with name: /test0
Duplicated url, with URL: /test1, with name: name-1
Duplicated url, with URL: /test3, with name: /test3, with description: description-1
Duplicated url, with URL: /test4, with name: /test4, with description: description-3

Ideally, this should also contain line numbers. I didn't dig deep into it, but I'm not sure if the Simple XML Framework library can provide them. That should be considered as another improvement.

Also, please note that currently, entries with the same href and different names (href="/test2" here) are not treated as a duplicate. I'm not a frequent AET user, so I'm not sure if the name serves some other important purpose, but if not, then the logic should probably be changed to treat every entry with identical href as a duplicate.
The documentation states that "If provided it [the name] should be unique for each test in the test suite.". However, I don't know what would be the purpose of having the same URL entered in the suite with different names.

Tested and accepted
version: 3.3.1.SNAPSHOT