[#302] pkg/session: Document default values set in NewToken

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

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

pkg/session/session.go

@@ -24,6 +24,15 @@ func NewTokenFromV2(tV2 *session.SessionToken) *Token {
 }
 
 // NewToken creates and returns blank Token.
+//
+// Defaults:
+//  - body: nil;
+//  - id: nil;
+//  - ownerId: nil;
+//  - sessionKey: nil;
+//  - exp: 0;
+//  - iat: 0;
+//  - nbf: 0;
 func NewToken() *Token {
 	return NewTokenFromV2(new(session.SessionToken))
 }

pkg/session/session_test.go

@@ -179,3 +179,24 @@ func TestToken_ToV2(t *testing.T) {
 		require.Nil(t, x.ToV2())
 	})
 }
+
+func TestNewToken(t *testing.T) {
+	t.Run("default values", func(t *testing.T) {
+		token := session.NewToken()
+
+		// check initial values
+		require.Nil(t, token.Signature())
+		require.Nil(t, token.OwnerID())
+		require.Nil(t, token.SessionKey())
+		require.Nil(t, token.ID())
+		require.Zero(t, token.Exp())
+		require.Zero(t, token.Iat())
+		require.Zero(t, token.Nbf())
+
+		// convert to v2 message
+		tokenV2 := token.ToV2()
+
+		require.Nil(t, tokenV2.GetSignature())
+		require.Nil(t, tokenV2.GetBody())
+	})
+}