tests: make tests requiring a delay to pass, more robust

* tests/init.cfg: Introduce a retry_delay_() function to
repeatedly call a test function that requires a delay.
This delay can now be shorter for the common case on fast
systems, but will double until a configurable limit it reached
before failing on slower systems.
* tests/dd/reblock: Use retry_delay_.
* tests/misc/cat-buf: Likewise.
* tests/misc/stdbuf: Likewise.
* tests/tail-2/F-vs-rename: Likewise.
* tests/tail-2/flush-initial: Likewise.
* tests/tail-2/tail-n0f: Likewise.
* tests/tail-2/wait: Likewise.
* test/dd/misc: Comment that delay is needed to trigger failure.

1 files changed, 12 insertions, 6 deletions

diff --git a/tests/tail-2/tail-n0f b/tests/tail-2/tail-n0f
index 0ff3a3d01..6a9b59c37 100755
--- a/tests/tail-2/tail-n0f
+++ b/tests/tail-2/tail-n0f
@@ -39,12 +39,18 @@ for inotify in ---disable-inotify ''; do
     for c_or_n in c n; do
       tail --sleep=4 -${c_or_n} 0 -f $inotify $file &
       pid=$!
-      sleep .5
-      state=$(get_process_status_ $pid)
-      case $state in
-        S*) ;;
-        *) echo $0: process in unexpected state: $state 1>&2; fail=1 ;;
-      esac
+      tail_sleeping()
+      {
+        local delay="$1"; sleep $delay
+        state=$(get_process_status_ $pid)
+        case $state in
+          S*) ;;
+          *) return 1;;
+        esac
+      }
+      # Wait up to 1.5s for tail to sleep
+      retry_delay_ tail_sleeping .1 4 ||
+        { echo $0: process in unexpected state: $state >&2; fail=1; }
       kill $pid
     done
   done