// the errors that gcc prints. That is, this function expects
// gcc to fail.
func (p *Package) gccErrors(stdin []byte, extraArgs ...string) string {
	// TODO(rsc): require failure
	args := p.gccCmd()

	// Optimization options can confuse the error messages; remove them.
	nargs := make([]string, 0, len(args)+len(extraArgs))
	for _, arg := range args {
		if !strings.HasPrefix(arg, "-O") {

	{"012abcba210", "\xffb", 6},
	{"012\x80bcb\x80210", "\xffb", 7},
	{"0123456\xcf\x80abc", "\xcfb\x80", 10},
}

// Execute f on each test case.  funcName should be the name of f; it's used
// in failure reports.
func runIndexTests(t *testing.T, f func(s, sep []byte) int, funcName string, testCases []BinOpTest) {
	for _, test := range testCases {
		a := []byte(test.a)
		b := []byte(test.b)
		actual := f(a, b)