tests: avoid a race in tail --retry testing

Prompted by the continuous integration build failure at:
http://hydra.nixos.org/build/5221053

* tests/tail-2/retry.sh: Ensure the 'out' file is truncated,
as it's used to arbitrate the run order of commands.
Relying on the truncation in the background tail command
is racy because the truncation can occur after the fork
of the background shell and thus wait4lines would not wait
for output to occur in 'out', which would mean that the
'missing' file could be populated by the time tail(1)
gets to process it.

diff --git a/tests/tail-2/retry.sh b/tests/tail-2/retry.sh
index d56d4c169667e674fdc5229bc9f0dbbe69be8eb7..7ba773475786398b6204c6d5c48fca09ab485596 100644 (file)
--- a/tests/tail-2/retry.sh
+++ b/tests/tail-2/retry.sh
@@ -26,7 +26,7 @@ wait4lines_ ()
 {
   local delay=$1
   local elc=$2   # Expected line count.
-  [ $( wc -l < out ) -ge $elc ] || { sleep $delay; return 1; }
+  [ "$( wc -l < out )" -ge "$elc" ] || { sleep $delay; return 1; }
 }
 
 # === Test:
@@ -44,9 +44,11 @@ grep -F 'tail: warning: --retry ignored' out || fail=1
 
 # === Test:
 # Ensure that "tail --retry --follow=name" waits for the file to appear.
+# Clear 'out' so that we can check its contents without races
+:>out                           || framework_failure_
 timeout 10 tail -s.1 --follow=name --retry missing >out 2>&1 & pid=$!
 retry_delay_ wait4lines_ .1 6 1 || fail=1  # Wait for "cannot open" error.
-echo "X" > missing              || fail=1  # Write "X" into 'missing'.
+echo "X" > missing              || fail=1
 retry_delay_ wait4lines_ .1 6 3 || fail=1  # Wait for the expected output.
 kill $pid
 wait $pid
@@ -55,14 +57,14 @@ wait $pid
 grep -F 'cannot open' out           || { fail=1; cat out; }
 grep -F 'has become accessible' out || { fail=1; cat out; }
 grep '^X$' out                      || { fail=1; cat out; }
-rm -f missing out                   || fail=1
+rm -f missing out                   || framework_failure_
 
 # === Test:
 # Ensure that "tail --retry --follow=descriptor" waits for the file to appear.
 # tail-8.21 failed at this (since the implementation of the inotify support).
 timeout 10 tail -s.1 --follow=descriptor --retry missing >out 2>&1 & pid=$!
 retry_delay_ wait4lines_ .1 6 2 || fail=1  # Wait for "cannot open" error.
-echo "X" > missing              || fail=1  # Write "X" into 'missing'.
+echo "X" > missing              || fail=1
 retry_delay_ wait4lines_ .1 6 4 || fail=1  # Wait for the expected output.
 kill $pid
 wait $pid
@@ -73,7 +75,7 @@ grep -F 'retry only effective for the initial open' out \
 grep -F 'cannot open' out  || { fail=1; cat out; }
 grep -F 'has appeared' out || { fail=1; cat out; }
 grep '^X$' out             || { fail=1; cat out; }
-rm -f missing out          || fail=1
+rm -f missing out          || framework_failure_
 
 # === Test:
 # Ensure that tail --follow=descriptor --retry exits when the file appears
@@ -91,7 +93,7 @@ grep -F 'cannot open' out                      || { fail=1; cat out; }
 grep -F 'replaced with an untailable file' out || { fail=1; cat out; }
 grep -F 'no files remaining' out               || { fail=1; cat out; }
 [ $rc = 1 ]                                    || { fail=1; cat out; }
-rm -fd missing out                             || fail=1
+rm -fd missing out                             || framework_failure_
 
 # === Test:
 # Ensure that --follow=descriptor (without --retry) does *not wait* for the