Is tails tested against DNS leaks?

Yes

Recently I have read a comparison between popular anon distros that suggests Tails can leak DNS.

Link please

Is that true?

Not that I'm aware of. Is this FUD?

Is tails tested against DNS leaks?

Tails is indeed tested against DNS leaks (the actual test checks whether all network traffic is routed through Tor, which implies no DNS leaks). For more information about what Tails does w.r.t. DNS, see the DNS section of the Tor enforcement design.

Recently I have read a comparison between popular anon distros that suggests Tails can leak DNS.

Link please

Seconded.

@2 & 3: Scroll down to security on the following link. Other weaknesses of Tails security are also mentioned:

http://sourceforge.net/p/whonix/wiki/Comparison%20with%20Others/

Security Whonix Tails TBB

IP/DNS protocol leak protection Full ^1^ Depends ^5^ Depends ^5^

^5^ See first example of Whonix security in real world. When applications in Tails are configured wrong, due to a bug in Tails or the application, IP can leak. Quoted from the Tails Security Page: "Until an audit of the bundled network applications is done, information leakages at the protocol level should be considered as − at the very least − possible."