e= s='foo'
failures=''
ok=''

testcase() {
	code="$1"
	expected="$2"
	oIFS="$IFS"
	eval "$code"
	IFS='|'
	result="$#|$*"
	IFS="$oIFS"
	if [ "x$result" = "x$expected" ]; then
		ok=x$ok
	else
		failures=x$failures
		echo "For $code, expected $expected actual $result"
	fi
}

testcase 'set -- ${s+a b}'			'2|a|b'
testcase 'set -- ${e:-a b}'			'2|a|b'

test "x$failures" = x