[#140] sdk: Define checksum type

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/checksum_test.go

@@ -0,0 +1,40 @@
+package pkg
+
+import (
+	"crypto/rand"
+	"crypto/sha256"
+	"testing"
+
+	"github.com/nspcc-dev/neofs-api-go/v2/refs"
+	"github.com/stretchr/testify/require"
+)
+
+func TestChecksum(t *testing.T) {
+	c := NewChecksum()
+
+	cSHA256 := [sha256.Size]byte{}
+	_, _ = rand.Read(cSHA256[:])
+
+	c.SetSHA256(cSHA256)
+
+	require.Equal(t, ChecksumSHA256, c.GetType())
+	require.Equal(t, cSHA256[:], c.GetSum())
+
+	cV2 := c.ToV2()
+
+	require.Equal(t, refs.SHA256, cV2.GetType())
+	require.Equal(t, cSHA256[:], cV2.GetSum())
+
+	cTZ := [64]byte{}
+	_, _ = rand.Read(cSHA256[:])
+
+	c.SetTillichZemor(cTZ)
+
+	require.Equal(t, ChecksumTZ, c.GetType())
+	require.Equal(t, cTZ[:], c.GetSum())
+
+	cV2 = c.ToV2()
+
+	require.Equal(t, refs.TillichZemor, cV2.GetType())
+	require.Equal(t, cTZ[:], cV2.GetSum())
+}