[#140] sdk/object: Define Attribute type

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

pkg/object/attribute_test.go

@@ -0,0 +1,23 @@
+package object
+
+import (
+	"testing"
+
+	"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.GetKey())
+	require.Equal(t, val, a.GetValue())
+
+	aV2 := a.ToV2()
+
+	require.Equal(t, key, aV2.GetKey())
+	require.Equal(t, val, aV2.GetValue())
+}