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.

1 files changed, 5 insertions, 3 deletions

diff --git a/tests/mv/no-target-dir.sh b/tests/mv/no-target-dir.sh
index 9f8ece0a1..d7bca59b1 100755
--- a/tests/mv/no-target-dir.sh
+++ b/tests/mv/no-target-dir.sh
@@ -20,6 +20,8 @@
 . "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
 print_ver_ mv
 
+LS_FAILURE=2
+
 mkdir -p d/sub empty src d2/sub e2 || framework_failure_
 touch f || framework_failure_
 
@@ -35,15 +37,15 @@ mv a b ||
 mv -fT d empty || fail=1
 
 # Ensure that the source, d, is gone.
-ls -d d > /dev/null 2>&1 && fail=1
+returns_ $LS_FAILURE ls -d d > /dev/null 2>&1 || fail=1
 
 # Ensure that the dest dir now has a subdirectory.
 test -d empty/sub || fail=1
 
 # rename must fail, since the dest is non-empty.
-mv -fT src d2 2> /dev/null && fail=1
+returns_ 1 mv -fT src d2 2> /dev/null || fail=1
 
 # rename must fail, since the src is not a directory.
-mv -fT f e2 2> /dev/null && fail=1
+returns_ 1 mv -fT f e2 2> /dev/null || fail=1
 
 Exit $fail