func init() {
	testBytes = make([]byte, N)
	for i := 0; i < N; i++ {
		testBytes[i] = 'a' + byte(i%26)
	}
	testString = string(testBytes)
}

// Verify that contents of buf match the string s.
func check(t *testing.T, testname string, buf *Buffer, s string) {
	bytes := buf.Bytes()
	str := buf.String()
	if buf.Len() != len(bytes) {