This seems to fix the issue for me, but YMMV.

1 patch for repository http://darcs.net/screened:

patch 6cb8235250ece24247c0707256211b27f9bb6e3d
Author: Ben Franksen <benjamin.franksen@helmholtz-berlin.de>
Date:   Sun Jan  8 21:44:53 CET 2017
  * resolve issue2504: skip ssh tests that require password input

Attachments

• patch-preview.txt
• resolve-issue2504_-skip-ssh-tests-that-require-password-input.dpatch
• unnamed

Ignore this patch, it causes the ssh tests to be always skipped. That
was not the idea. (I was confused about the meaning of SSH_AUTH_SOCK)

Ok, here is an amended version. The idea is:

When testing whether ssh works (without user interaction, now), we call it
with -x (no X11 forwarding, which disables ssh-askpass) and also
-o=NumberofPasswordPrompts=0 (to disable command line prompt for password).

With this patch I can run

> ./dist/build/darcs-test/darcs-test -n --shell=no --unit=no --tests=ssh
Using darcs executable in
/home/ben/src/darcs/screened/dist/build/darcs/darcs
Locale encoding is UTF-8
network/ssh.sh (Darcs2) (PatienceDiff): [Success]
[...]

since I have an ssh agent running and already entered my passphrase.
However, when I (temporarily) disable the agent by unsetting SSH_AUTH_SOCK I
get 

> SSH_AUTH_SOCK= ./dist/build/darcs-test/darcs-test -n --shell=no --unit=no
--tests=ssh
Using darcs executable in
/home/ben/src/darcs/screened/dist/build/darcs/darcs
Locale encoding is UTF-8
network/ssh.sh (Darcs2) (PatienceDiff): [Skipped]
[...]

1 patch for repository http://darcs.net/screened:

patch cfac8592c40d18ce61da4521635e6f7e70f3c007
Author: Ben Franksen <benjamin.franksen@helmholtz-berlin.de>
Date:   Sun Jan  8 21:44:53 CET 2017
  * resolve issue2504: skip ssh tests that require password input

Attachments

• patch-preview.txt
• resolve-issue2504_-skip-ssh-tests-that-require-password-input.dpatch
• unnamed

Self accept (test system).