Limit test run-time.

test/testsuite.at

 AT_INIT ([PPM parallel tests])
 AT_COPYRIGHT(
 [
- Copyright  (C)  2010  Thomas Jahns <jahns@dkrz.de>
+ Copyright  (C)  2020  Thomas Jahns <jahns@dkrz.de>
 
  Redistribution and use in source and binary forms, with or without
  modification, are  permitted provided that the following conditions are
@@ -31,6 +31,14 @@ AT_COPYRIGHT(
  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 ])
 AT_COLOR_TESTS
+m4_define([acx_cpu_time_limit],[1800])
+AT_ARG_OPTION_ARG([time-limit],[AS_HELP_STRING([--time-limit],
+  [limit the run-time of tests via ulimit -t (default=]acx_cpu_time_limit[)])],
+  [AS_IF([expr "$at_optarg" : '\([0-9]*\|unlimited\)$' >/dev/null 2>&1],
+     [ulimit -t $at_optarg],
+     [echo "invalid cpu time limit $at_optarg" >&2
+      AS_EXIT(1)])],
+  [ulimit -t acx_cpu_time_limit])
 AT_BANNER([core routines])
 AT_SETUP([library abort])
 AT_KEYWORDS([core abort hybrid])