Automake AM_LDADD workaround

I want to set the same LDADD attribute (Unit test library) to a large number of targets (unit test C++ files). I first though that maybe automake has AM_LDADD variable to add that library to all the targets within the file but is not the case. In some mail list I found some short discussion asking to add it: http://ift.tt/1Nf7WTR

My question is, how do you deal with that? is it there any way to avoid manually adding LDADD attribute to each target?

So far my Makefile.am looks like:

 test1_SOURCES = ...
 test1_LDADD = -llibrary 
  ...
  ...
 test20_SOURCES = ...
 test20_LDADD = -llibrary