[#302] pkg/netmap: Document default values set in NewNodeInfo and NewNodeAttribute

Document field values of instance constructed via `NewNodeInfo` and `NewNodeAttribute`.
Assert the values in corresponding unit test.

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>

pkg/netmap/node_info.go

@@ -188,6 +188,11 @@ func (s NodeState) String() string {
 }
 
 // NewNodeAttribute creates and returns new NodeAttribute instance.
+//
+// Defaults:
+//  - key: "";
+//  - value: "";
+//  - parents: nil.
 func NewNodeAttribute() *NodeAttribute {
 	return NewNodeAttributeFromV2(new(netmap.Attribute))
 }
@@ -275,6 +280,12 @@ func (a *NodeAttribute) UnmarshalJSON(data []byte) error {
 }
 
 // NewNodeInfo creates and returns new NodeInfo instance.
+//
+// Defaults:
+//  - publicKey: nil;
+//  - address: "";
+//  - attributes nil;
+//  - state: 0.
 func NewNodeInfo() *NodeInfo {
 	return NewNodeInfoFromV2(new(netmap.NodeInfo))
 }
@@ -319,9 +330,17 @@ func (i *NodeInfo) SetAddress(addr string) {
 
 // Attributes returns list of the node attributes.
 func (i *NodeInfo) Attributes() []*NodeAttribute {
+	if i == nil {
+		return nil
+	}
+
 	as := (*netmap.NodeInfo)(i).
 		GetAttributes()
 
+	if as == nil {
+		return nil
+	}
+
 	res := make([]*NodeAttribute, 0, len(as))
 
 	for i := range as {

pkg/netmap/node_info_test.go

@@ -202,3 +202,41 @@ func TestNodeInfoEncoding(t *testing.T) {
 		require.Equal(t, i, i2)
 	})
 }
+
+func TestNewNodeAttribute(t *testing.T) {
+	t.Run("default values", func(t *testing.T) {
+		attr := NewNodeAttribute()
+
+		// check initial values
+		require.Empty(t, attr.Key())
+		require.Empty(t, attr.Value())
+		require.Nil(t, attr.ParentKeys())
+
+		// convert to v2 message
+		attrV2 := attr.ToV2()
+
+		require.Empty(t, attrV2.GetKey())
+		require.Empty(t, attrV2.GetValue())
+		require.Nil(t, attrV2.GetParents())
+	})
+}
+
+func TestNewNodeInfo(t *testing.T) {
+	t.Run("default values", func(t *testing.T) {
+		ni := NewNodeInfo()
+
+		// check initial values
+		require.Nil(t, ni.PublicKey())
+		require.Empty(t, ni.Address())
+		require.Nil(t, ni.Attributes())
+		require.Zero(t, ni.State())
+
+		// convert to v2 message
+		niV2 := ni.ToV2()
+
+		require.Nil(t, niV2.GetPublicKey())
+		require.Empty(t, niV2.GetAddress())
+		require.Nil(t, niV2.GetAttributes())
+		require.EqualValues(t, netmap.UnspecifiedState, niV2.GetState())
+	})
+}