Add Code Coverage

[jtenner]

[RedDwarfian]

The instances of default: assert(false); in the part of the Deserializer that handles the mapKeyValueEntryTable would never get called under normal circumstances. This would require malformed, or manually edited buffers to be passed in, in order to be tested. After discussion with @jtenner, we have agreed that @as-cover: ignoreing these defaults is the right move.