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

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

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

pkg/netmap/network_info.go

@@ -16,6 +16,10 @@ func NewNetworkInfoFromV2(iV2 *netmap.NetworkInfo) *NetworkInfo {
 }
 
 // NewNetworkInfo creates and initializes blank NetworkInfo.
+//
+// Defaults:
+//  - curEpoch: 0;
+//  - magicNum: 0.
 func NewNetworkInfo() *NetworkInfo {
 	return NewNetworkInfoFromV2(new(netmap.NetworkInfo))
 }

pkg/netmap/network_info_test.go

@@ -65,3 +65,17 @@ func TestNetworkInfo_ToV2(t *testing.T) {
 		require.Nil(t, x.ToV2())
 	})
 }
+
+func TestNewNetworkInfo(t *testing.T) {
+	ni := NewNetworkInfo()
+
+	// check initial values
+	require.Zero(t, ni.CurrentEpoch())
+	require.Zero(t, ni.MagicNumber())
+
+	// convert to v2 message
+	niV2 := ni.ToV2()
+
+	require.Zero(t, niV2.GetCurrentEpoch())
+	require.Zero(t, niV2.GetMagicNumber())
+}