tests(persistence): add missing test for author payload API

protocol/persistence_test.go

@@ -1517,3 +1517,28 @@ func TestSaveDiscordMessages(t *testing.T) {
 		require.EqualValues(t, "2", dm.Author.Id)
 	}
 }
+
+func TestUpdateDiscordMessageAuthorImage(t *testing.T) {
+
+	db, err := openTestDB()
+	require.NoError(t, err)
+	p := newSQLitePersistence(db)
+
+	require.NoError(t, p.SaveDiscordMessageAuthor(&protobuf.DiscordMessageAuthor{
+		Id:            "1",
+		Name:          "Testuser",
+		Discriminator: "1234",
+		Nickname:      "User",
+		AvatarUrl:     "http://example.com/profile.jpg",
+	}))
+
+	exists, err := p.HasDiscordMessageAuthor("1")
+	require.NoError(t, err)
+	require.True(t, exists)
+
+	err = p.UpdateDiscordMessageAuthorImage("1", []byte{0, 1, 2, 3})
+	require.NoError(t, err)
+	payload, err := p.GetDiscordMessageAuthorImagePayloadByID("1")
+	require.NoError(t, err)
+	require.Equal(t, []byte{0, 1, 2, 3}, payload)
+}