failures=''
ok=''

testcase() {
	code="$1"

	unset v
	eval ": \$($code)"

	if [ "${v:+bad}" = "" ]; then
		ok=x$ok
	else
		failures=x$failures
		echo "Failure for $code"
	fi
}

testcase ': ${v=0}'
testcase ': ${v:=0}'
testcase ': $((v=1))'
testcase ': $((v+=1))'
w='v=1'
testcase ': $(($w))'
testcase ': $((${$+v=1}))'
testcase ': $((v${$+=1}))'
testcase ': $((v $(echo =) 1))'
testcase ': $(($(echo $w)))'

test "x$failures" = x