test-framework-sh: Fix 'returns_' to not turn off tracing permanently

[Bruno Haible]

I'm debugging a unit test that consists of a dozen of shell statement groups,
each with a 'returns_ 1 ...' invocation. The log file shows an error message,
but no indication from which of the statement groups the error came. So,
naturally, I add a 'set -x' command near the beginning of the test file.
But it doesn't work: The first 'returns_ 1 ...' command turns off the 'x'
flag! - defeating the purpose of my 'set -x'.

This patch fixes it.


2024-06-11  Bruno Haible  <bruno@clisp.org>

        test-framework-sh: Fix 'returns_' to not turn off tracing permanently.
        * tests/init.sh (returns_): Restore tracing if it was enabled before.

diff --git a/tests/init.sh b/tests/init.sh
index 4689b6b758..2724f5ab67 100644
--- a/tests/init.sh
+++ b/tests/init.sh
@@ -594,6 +594,7 @@ fi
 #   returns_ 1 command ... || fail
 returns_ () {
   # Disable tracing so it doesn't interfere with stderr of the wrapped command
+  local is_tracing=`{ :; } 2>&1`
   { set +x; } 2>/dev/null
 
   local exp_exit="$1"
@@ -601,7 +602,8 @@ returns_ () {
   "$@"
   test $? -eq $exp_exit && ret_=0 || ret_=1
 
-  if test "$VERBOSE" = yes && test "$gl_set_x_corrupts_stderr_" = false; then
+  # Restore tracing if it was enabled.
+  if test -n "$is_tracing"; then
     set -x
   fi
   { return $ret_; } 2>/dev/null