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, 27 insertions, 0 deletions

diff --git a/tests/init.cfg b/tests/init.cfg
index aecdd5a2c..232cb9bae 100644
--- a/tests/init.cfg
+++ b/tests/init.cfg
@@ -357,4 +357,31 @@ working_umask_or_skip_()
   esac
 }
 
+# Continually retry a function requiring a sufficient delay to _pass_
+#     Example: retry_delay dd_reblock_1 .1 6
+# This example will call the dd_reblock_1 function with
+# an initial delay of .1 second and call it at most 6 times
+# with a max delay of 3.2s (doubled each time), or a total of 6.3s
+# Note ensure you do _not_ quote the parameter to GNU sleep in
+# your function, as it may contain separate values that `sleep`
+# needs to accumulate.
+retry_delay_()
+{
+  local test_func=$1
+  local init_delay=$2
+  local max_n_tries=$3
+
+  local attempt=1
+  local num_sleeps=$attempt
+  local time_fail
+  while test $attempt -le $max_n_tries; do
+    local delay=$($AWK -v n=$num_sleeps -v s="$init_delay" \
+                  'BEGIN { for (i=0;i<n;i++) t = s" "t; print t }')
+    "$test_func" "$delay" && { time_fail=0; break; } || time_fail=1
+    attempt=$(expr $attempt + 1)
+    num_sleeps=$(expr $num_sleeps '*' 2)
+  done
+  test "$time_fail" = 0
+}
+
 sanitize_path_