tests: improve diagnostics when asserting empty files

* tests/chmod/c-option.sh: Use `compare /dev/null ... || fail=1`
rather than `test -s ... && fail=1`, so that the file contents
are output, thus improving diagnostics for failing tests.
* tests/cp/acl.sh: Likewise.
* tests/cp/cp-a-selinux.sh: Likewise.
* tests/cp/cp-mv-enotsup-xattr.sh: Likewise.
* tests/cp/reflink-perm.sh: Likewise.
* tests/dd/misc.sh: Likewise.
* tests/misc/env-null.sh: Likewise.
* tests/misc/env.sh: Likewise.
* tests/misc/nice.sh: Likewise.
* tests/misc/nohup.sh: Likewise.
* tests/misc/printenv.sh: Likewise.
* tests/misc/xattr.sh: Likewise.
* tests/mv/update.sh: Likewise.
* tests/rm/deep-2.sh: Likewise.
* tests/rm/read-only.sh: Likewise.
* tests/split/r-chunk.sh: Likewise.
* tests/tail-2/follow-stdin.sh: Likewise.
* tests/tail-2/inotify-race.sh: Likewise.
* tests/tail-2/wait.sh: Likewise.
* tests/touch/no-dereference.sh: Likewise.

* cfg.mk (sc_prohibit_test_empty:): New syntax-check.
* tests/cp/proc-zero-len.sh: Adjust to avoid false syntax-check failure.
* tests/cp/proc-zero-len.sh: Likewise.
* tests/mv/part-symlink.sh: Likewise.
* tests/tail-2/infloop-1.sh: Likewise.

5 files changed, 16 insertions, 13 deletions

diff --git a/tests/cp/acl.sh b/tests/cp/acl.sh
index 0dc9f882d..36a5d298c 100755
--- a/tests/cp/acl.sh
+++ b/tests/cp/acl.sh
@@ -53,7 +53,7 @@ test "$acl1" = "$acl2" || fail=1
 echo > a/file || framework_failure_ # add some data
 test -s a/file || framework_failure_
 cp -p --attributes-only a/file b/ || fail=1
-test -s b/file && fail=1
+compare /dev/null b/file || fail=1
 acl2=$(cd b && getfacl file) || framework_failure_
 test "$acl1" = "$acl2" || fail=1
 
diff --git a/tests/cp/cp-a-selinux.sh b/tests/cp/cp-a-selinux.sh
index 3ab7e0e28..db0d68930 100755
--- a/tests/cp/cp-a-selinux.sh
+++ b/tests/cp/cp-a-selinux.sh
@@ -37,7 +37,8 @@ cp -a c d 2>err || framework_failure_
 cp --preserve=context c e || framework_failure_
 cp --preserve=all c f || framework_failure_
 ls -Z d | grep $ctx || fail=1
-test -s err && fail=1   #there must be no stderr output for -a
+# there must be no stderr output for -a
+compare /dev/null err || fail=1
 ls -Z e | grep $ctx || fail=1
 ls -Z f | grep $ctx || fail=1
 
@@ -116,7 +117,7 @@ echo > g                                     || framework_failure_
 # succeed (giving no diagnostics), yet leaving the destination file empty.
 cp -a f g 2>err || fail=1
 test -s g       || fail=1     # The destination file must not be empty.
-test -s err     && fail=1     # There must be no stderr output.
+compare /dev/null err || fail=1
 
 # =====================================================
 # Here, we expect cp to succeed and not warn with "Operation not supported"
@@ -151,7 +152,7 @@ echo > g
 # security context through NFS or a mount with fixed context.
 cp --preserve=context f g 2> out && fail=1
 # Here, we *do* expect the destination to be empty.
-test -s g && fail=1
+compare /dev/null g || fail=1
 sed "s/ .g'.*//" out > k
 mv k out
 compare exp out || fail=1
@@ -161,7 +162,7 @@ echo > g
 # Check if -a option doesn't silence --preserve=context option diagnostics
 cp -a --preserve=context f g 2> out2 && fail=1
 # Here, we *do* expect the destination to be empty.
-test -s g && fail=1
+compare /dev/null g || fail=1
 sed "s/ .g'.*//" out2 > k
 mv k out2
 compare exp out2 || fail=1
diff --git a/tests/cp/cp-mv-enotsup-xattr.sh b/tests/cp/cp-mv-enotsup-xattr.sh
index 11809892a..f46977b60 100755
--- a/tests/cp/cp-mv-enotsup-xattr.sh
+++ b/tests/cp/cp-mv-enotsup-xattr.sh
@@ -69,19 +69,19 @@ grep -F "$xattr_pair" out_a >/dev/null \
 # This should pass without diagnostics
 cp -a xattr/a noxattr/ 2>err || fail=1
 test -s noxattr/a   || fail=1  # destination file must not be empty
-test -s err         && fail=1  # there must be no stderr output
+compare /dev/null err || fail=1
 
 rm -f err noxattr/a
 
 # This should pass without diagnostics (new file)
 cp --preserve=all xattr/a noxattr/ 2>err || fail=1
 test -s noxattr/a   || fail=1  # destination file must not be empty
-test -s err         && fail=1  # there must be no stderr output
+compare /dev/null err || fail=1
 
 # This should pass without diagnostics (existing file)
 cp --preserve=all xattr/a noxattr/ 2>err || fail=1
 test -s noxattr/a   || fail=1  # destination file must not be empty
-test -s err         && fail=1  # there must be no stderr output
+compare /dev/null err || fail=1
 
 rm -f err noxattr/a
 
@@ -104,7 +104,7 @@ rm -f err noxattr/a
 # This should pass without diagnostics
 mv xattr/a noxattr/ 2>err || fail=1
 test -s noxattr/a         || fail=1  # destination file must not be empty
-test -s err               && fail=1  # there must be no stderr output
+compare /dev/null err || fail=1
 
 # This should pass and copy xattrs of the symlink
 # since the xattrs used here are not in the 'user.' namespace.
diff --git a/tests/cp/proc-zero-len.sh b/tests/cp/proc-zero-len.sh
index 3369cfb3c..3fcd5aab1 100755
--- a/tests/cp/proc-zero-len.sh
+++ b/tests/cp/proc-zero-len.sh
@@ -37,8 +37,10 @@ cp $f exp 2>err \
 # Don't simply compare contents; they might differ,
 # e.g., if CPU freq changes between cat and cp invocations.
 # Instead, simply compare whether they're both nonempty.
-test -s out && { rm -f out; echo nonempty > out; }
-test -s exp && { rm -f exp; echo nonempty > exp; }
+test -s out \
+  && { rm -f out; echo nonempty > out; }
+test -s exp \
+  && { rm -f exp; echo nonempty > exp; }
 
 compare exp out || fail=1
 
diff --git a/tests/cp/reflink-perm.sh b/tests/cp/reflink-perm.sh
index 52f83fce1..52f5e2576 100755
--- a/tests/cp/reflink-perm.sh
+++ b/tests/cp/reflink-perm.sh
@@ -38,8 +38,8 @@ test copy -nt file && fail=1
 # Ensure that --attributes-only overrides --reflink completely
 echo > file2 # file with data
 cp --reflink=auto --preserve --attributes-only file2 empty_copy || fail=1
-test -s empty_copy && fail=1
+compare /dev/null empty_copy || fail=1
 cp --reflink=always --preserve --attributes-only file2 empty_copy || fail=1
-test -s empty_copy && fail=1
+compare /dev/null empty_copy || fail=1
 
 Exit $fail