[#302] pkg/netmap: Document default values set in NewSelector

Document field values of instance constructed via `NewSelector`.
Assert the values in corresponding unit test.

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

pkg/netmap/selector.go

@@ -156,6 +156,13 @@ func (c *Context) getSelectionBase(s *Selector) []nodeAttrPair {
 }
 
 // NewSelector creates and returns new Selector instance.
+//
+// Defaults:
+//  - name: "";
+//  - attribute: "";
+//  - filter: "";
+//  - clause: ClauseUnspecified;
+//  - count: 0.
 func NewSelector() *Selector {
 	return NewSelectorFromV2(new(netmap.Selector))
 }

pkg/netmap/selector_test.go

@@ -507,3 +507,25 @@ func TestNewSelectorFromV2(t *testing.T) {
 		require.Equal(t, sV2, s.ToV2())
 	})
 }
+
+func TestNewSelector(t *testing.T) {
+	t.Run("default values", func(t *testing.T) {
+		s := NewSelector()
+
+		// check initial values
+		require.Zero(t, s.Count())
+		require.Equal(t, ClauseUnspecified, s.Clause())
+		require.Empty(t, s.Attribute())
+		require.Empty(t, s.Name())
+		require.Empty(t, s.Filter())
+
+		// convert to v2 message
+		sV2 := s.ToV2()
+
+		require.Zero(t, sV2.GetCount())
+		require.Equal(t, netmap.UnspecifiedClause, sV2.GetClause())
+		require.Empty(t, sV2.GetAttribute())
+		require.Empty(t, sV2.GetName())
+		require.Empty(t, sV2.GetFilter())
+	})
+}