refactor(countrw): move to iout

iout/copy_range_test.go

@@ -0,0 +1,42 @@
+package iout_test
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/matryer/is"
+	"go.senan.xyz/gonic/iout"
+)
+
+func TestCopyRange(t *testing.T) {
+	t.Parallel()
+	is := is.New(t)
+
+	realLength := 50
+	cr := func(start, length int64) []byte {
+		is.Helper()
+		var data []byte
+		for i := 0; i < realLength; i++ {
+			data = append(data, byte(i%10))
+		}
+		var buff bytes.Buffer
+		is.NoErr(iout.CopyRange(&buff, bytes.NewReader(data), start, length))
+		return buff.Bytes()
+	}
+
+	// range
+	is.Equal(len(cr(0, 50)), 50)
+	is.Equal(len(cr(10, 10)), 10)
+	is.Equal(cr(10, 10)[0], byte(0))
+	is.Equal(cr(10, 10)[5], byte(5))
+	is.Equal(cr(25, 35)[0], byte(5))
+	is.Equal(cr(25, 35)[5], byte(0))
+
+	// 0 padding
+	is.Equal(len(cr(0, 5000)), 5000)
+	is.Equal(cr(0, 5000)[50:], make([]byte, 5000-50))
+
+	// no bound
+	is.Equal(len(cr(0, 0)), 50)
+	is.Equal(len(cr(50, 0)), 0)
+}