[#64] object: move package from neofs-api-go

Also, remove deprecated method.

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

object/attribute_test.go

@@ -0,0 +1,82 @@
+package object
+
+import (
+	"testing"
+
+	"github.com/nspcc-dev/neofs-api-go/v2/object"
+	"github.com/stretchr/testify/require"
+)
+
+func TestAttribute(t *testing.T) {
+	key, val := "some key", "some value"
+
+	a := NewAttribute()
+	a.SetKey(key)
+	a.SetValue(val)
+
+	require.Equal(t, key, a.Key())
+	require.Equal(t, val, a.Value())
+
+	aV2 := a.ToV2()
+
+	require.Equal(t, key, aV2.GetKey())
+	require.Equal(t, val, aV2.GetValue())
+}
+
+func TestAttributeEncoding(t *testing.T) {
+	a := NewAttribute()
+	a.SetKey("key")
+	a.SetValue("value")
+
+	t.Run("binary", func(t *testing.T) {
+		data, err := a.Marshal()
+		require.NoError(t, err)
+
+		a2 := NewAttribute()
+		require.NoError(t, a2.Unmarshal(data))
+
+		require.Equal(t, a, a2)
+	})
+
+	t.Run("json", func(t *testing.T) {
+		data, err := a.MarshalJSON()
+		require.NoError(t, err)
+
+		a2 := NewAttribute()
+		require.NoError(t, a2.UnmarshalJSON(data))
+
+		require.Equal(t, a, a2)
+	})
+}
+
+func TestNewAttributeFromV2(t *testing.T) {
+	t.Run("from nil", func(t *testing.T) {
+		var x *object.Attribute
+
+		require.Nil(t, NewAttributeFromV2(x))
+	})
+}
+
+func TestAttribute_ToV2(t *testing.T) {
+	t.Run("nil", func(t *testing.T) {
+		var x *Attribute
+
+		require.Nil(t, x.ToV2())
+	})
+}
+
+func TestNewAttribute(t *testing.T) {
+	t.Run("default values", func(t *testing.T) {
+		a := NewAttribute()
+
+		// check initial values
+		require.Empty(t, a.Key())
+		require.Empty(t, a.Value())
+
+		// convert to v2 message
+		aV2 := a.ToV2()
+
+		require.Empty(t, aV2.GetKey())
+		require.Empty(t, aV2.GetValue())
+	})
+}