tests: add extra protection against unexpected exits

Many tests use `program ... && fail=1` to ensure expected
error situations are indicated.  However that would mask
an unexpected exit (like a crash).  Therefore explicitly
check the expected exit code.
Note where error messages are also verified, the extra
protection is not added.

* tests/init.sh (returns_): A new helper function to
check the return code of a command, and used
throughout the tests.
* cfg.mk (sc_prohibit_and_fail_1): Add a syntax check
to avoid new instances of this issue.

4 files changed, 11 insertions, 6 deletions

diff --git a/tests/id/context.sh b/tests/id/context.sh
index 754d0c3ba..b1aefe73f 100755
--- a/tests/id/context.sh
+++ b/tests/id/context.sh
@@ -26,7 +26,10 @@ id | grep context= >/dev/null || fail=1
 
 # Check with specified user, no context string should be present.
 # But if the current user is nameless, skip this part.
-id -nu > /dev/null \
-  && id $(id -nu) | grep context= >/dev/null && fail=1
+name=$(id -nu) || { test $? -ne 1 && fail=1; }
+if test "$name"; then
+  id "$name" > id_name || fail=1
+  grep context= id_name >/dev/null && fail=1
+fi
 
 Exit $fail
diff --git a/tests/id/gnu-zero-uids.sh b/tests/id/gnu-zero-uids.sh
index edd74f7dd..c2ee6cfb3 100755
--- a/tests/id/gnu-zero-uids.sh
+++ b/tests/id/gnu-zero-uids.sh
@@ -24,6 +24,6 @@ require_gnu_
 sush - true || skip_ "the 'sush' command does not work"
 
 # Run 'id' with zero UIDs.  It should exit with a non-zero status.
-sush - id > out && fail=1
+returns_ 1 sush - id > out || fail=1
 
 Exit $fail
diff --git a/tests/id/uid.sh b/tests/id/uid.sh
index c0766b321..e7a838586 100755
--- a/tests/id/uid.sh
+++ b/tests/id/uid.sh
@@ -22,7 +22,7 @@ uid=$(id -u) || fail=1
 user=$(id -nu) || fail=1
 
 # Ensure the empty user spec is discarded
-id '' && fail=1
+returns_ 1 id '' || fail=1
 
 for mode in '' '-G' '-g'; do
   id $mode $user > user_out || fail=1 # lookup name for comparison
diff --git a/tests/id/zero.sh b/tests/id/zero.sh
index a67a789e2..7bee3a644 100755
--- a/tests/id/zero.sh
+++ b/tests/id/zero.sh
@@ -51,8 +51,10 @@ while read u ; do
       printf '\n%s: ' "id -${o}${n}[z] $u" >> out || framework_failure_
       # There may be no name corresponding to an id, so don't check
       # exit status when in name lookup mode
-      id -${o}${n}  $u >> exp || { test -z "$n" && fail=1; }
-      id -${o}${n}z $u  > tmp || { test -z "$n" && fail=1; }
+      id -${o}${n}  $u >> exp ||
+        { test $? -ne 1 || test -z "$n" && fail=1; }
+      id -${o}${n}z $u  > tmp ||
+        { test $? -ne 1 || test -z "$n" && fail=1; }
       head -c-1 < tmp >> out || framework_failure_
     done
   done