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.

2 files changed, 29 insertions, 13 deletions

diff --git a/tests/dd/misc b/tests/dd/misc
index 7caacbc7b..ddd7bbd9e 100755
--- a/tests/dd/misc
+++ b/tests/dd/misc
@@ -87,6 +87,8 @@ fi
 outbytes=`echo x | dd bs=3 ibs=10 obs=10 conv=sync 2>/dev/null | wc -c`
 test "$outbytes" -eq 3 || fail=1
 
+# A delay is required to trigger a failure.
+# There might be some missed failures but it's unlikely.
 (echo a; sleep .1; echo b) \
   | env LC_ALL=C dd bs=4 status=noxfer iflag=fullblock >out 2>err || fail=1
 printf 'a\nb\n' > out_ok || framework_failure
diff --git a/tests/dd/reblock b/tests/dd/reblock
index 4a487663b..9c9b0f85f 100755
--- a/tests/dd/reblock
+++ b/tests/dd/reblock
@@ -45,18 +45,32 @@ EOF
 # from each printf separately.
 mkfifo dd.fifo || framework_failure
 
-# ensure that dd reblocks when bs= is not specified
-dd ibs=3 obs=3 if=dd.fifo > out 2> err&
-(printf 'ab'; sleep .2; printf 'cd') > dd.fifo
-wait #for dd to complete
-sed 's/,.*//' err > k && mv k err
-compare err exp-reblock || fail=1
-
-# Demonstrate that bs=N supersedes even following ibs= and obs= settings.
-dd bs=3 ibs=1 obs=1 if=dd.fifo > out 2> err&
-(printf 'ab'; sleep .2; printf 'cd') > dd.fifo
-wait #for dd to complete
-sed 's/,.*//' err > k && mv k err
-compare err exp-no-reblock || fail=1
+dd_reblock_1()
+{
+  local delay="$1"
+
+  # ensure that dd reblocks when bs= is not specified
+  dd ibs=3 obs=3 if=dd.fifo > out 2> err&
+  (printf 'ab'; sleep $delay; printf 'cd') > dd.fifo
+  wait #for dd to complete
+  sed 's/,.*//' err > k && mv k err
+  compare err exp-reblock
+}
+
+retry_delay_ dd_reblock_1 .1 6 || fail=1
+
+dd_reblock_2()
+{
+  local delay="$1"
+
+  # Demonstrate that bs=N supersedes even following ibs= and obs= settings.
+  dd bs=3 ibs=1 obs=1 if=dd.fifo > out 2> err&
+  (printf 'ab'; sleep $delay; printf 'cd') > dd.fifo
+  wait #for dd to complete
+  sed 's/,.*//' err > k && mv k err
+  compare err exp-no-reblock
+}
+
+retry_delay_ dd_reblock_2 .1 6 || fail=1
 
 Exit $fail