In 0.15 (or current master) try running 

  % TERM=dump make test

At least for me and the Debian build daemons, this causes the run to end
with

  PASS   Show message: json, utf-8
  FATAL: Unexpected exit with code 1
  make: *** [test] Error 124

This is much worse than a test failure since it causes the build to exit
with non-zero status.

I have temporarily disabled running the test suite in the debian
packaging, but this is obviously not a good permanent solution.

Apparently the problem is on the line 

 TERM=$ORIGINAL_TERM dtach -n "$TEST_TMPDIR/emacs-dtach-socket.$$" 

It would be easy to hardcode the TERM for dtach, but I'm not sure if
there is some advantage to testing with the user's actual term? Also, I
guess we'd have to be careful the chosen terminal type is portable.

d