-warn_() { echo "$@" 1>&$stderr_fileno_; }
-fail_() { warn_ "$ME_: failed test: $@"; Exit 1; }
-skip_() { warn_ "$ME_: skipped test: $@"; Exit 77; }
-framework_failure_() { warn_ "$ME_: set-up failure: $@"; Exit 99; }
+# Note that correct expansion of "$*" depends on IFS starting with ' '.
+# Always write the full diagnostic to stderr.
+# When stderr_fileno_ is not 2, also emit the first line of the
+# diagnostic to that file descriptor.
+warn_ ()
+{
+ # If IFS does not start with ' ', set it and emit the warning in a subshell.
+ case $IFS in
+ ' '*) printf '%s\n' "$*" >&2
+ test $stderr_fileno_ = 2 \
+ || { printf '%s\n' "$*" | sed 1q >&$stderr_fileno_ ; } ;;
+ *) (IFS=' '; warn_ "$@");;
+ esac
+}
+fail_ () { warn_ "$ME_: failed test: $@"; Exit 1; }
+skip_ () { warn_ "$ME_: skipped test: $@"; Exit 77; }
+fatal_ () { warn_ "$ME_: hard error: $@"; Exit 99; }
+framework_failure_ () { warn_ "$ME_: set-up failure: $@"; Exit 99; }