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

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

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

pkg/netmap/replica.go

@@ -8,6 +8,10 @@ import (
 type Replica netmap.Replica
 
 // NewReplica creates and returns new Replica instance.
+//
+// Defaults:
+//  - count: 0;
+//  - selector: "".
 func NewReplica() *Replica {
 	return NewReplicaFromV2(new(netmap.Replica))
 }

pkg/netmap/replica_test.go

@@ -81,3 +81,19 @@ func TestReplica_ToV2(t *testing.T) {
 		require.Nil(t, x.ToV2())
 	})
 }
+
+func TestNewReplica(t *testing.T) {
+	t.Run("default values", func(t *testing.T) {
+		r := NewReplica()
+
+		// check initial values
+		require.Zero(t, r.Count())
+		require.Empty(t, r.Selector())
+
+		// convert to v2 message
+		rV2 := r.ToV2()
+
+		require.Zero(t, rV2.GetCount())
+		require.Empty(t, rV2.GetSelector())
+	})
+}