Built a comprehensive xUnit test suite that immediately caught real data bugs, merged a major codebase refactor from the other dev, and created a full codebase index for AI-assisted cross-dev collaboration. The MMO prototype now has automated validation covering every JSON data file, skill system, combat mechanics, and inventory operations.

The Test Suite That Pays for Itself Immediately

The whole reason for building tests was the previous session's crashes — a DamageType set to "Magic" instead of "Arcane" in Items.json crashed the game at runtime, and the only way to catch it was to play through character creation and wait for the deserializer to explode. So we built 101 xUnit tests across four files: DataValidationTests validates all 17 JSON data files deserialize cleanly, checks for duplicate IDs, validates cross-references (loot tables → items, shops → items, recipes → items, spawn zones → enemies), and enforces value ranges on stats. SkillSystemTests covers progression math, specialty XP bonuses, level caps, and save data round-trips. CombatSystemTests validates stat blocks, socket counts by rarity, and collision size fallbacks. InventoryTests exercises the multi-container grid inventory, bank storage, and item instance uniqueness. The duplicate ID test caught two real bugs on its very first run: a duplicate potion_mana from our session and a duplicate weapon_staff_training from the merge.

Merging the Great Refactor

The other dev landed a substantial refactor on main while we were building tests: GameplayScreen was decomposed into overworld service classes (OverworldBootstrap, OverworldSaveService, OverworldSpawnService, OverworldInteractionService, OverworldUiFactory), Player was split into partial classes (Actions, Combat, Movement), and all the old design docs were replaced with a focused set. The merge hit 8 file conflicts. Since the refactored code already incorporated our character creation and startup features, we took the other dev's versions across the board. One post-merge issue: both branches had independently added SetSpecialtyBonus/HasSpecialtyBonus methods, producing duplicates. Tests passed clean after deduplication.

Codebase Index for AI Navigation

With two devs (and their respective AI assistants) working in parallel, we needed a shared understanding of where everything lives. Created docs/codebase_index.md: a complete file map covering all 105 source files, 24 JSON data files, module dependency flow, key enum catalogs, and a cross-reference routing table ("adding a new spell? Define in Spells.json, runtime in SpellBook.cs, UI in WizardGuildPanel + SpellBookPanel"). Restored CLAUDE.md at the project root as the AI entry point, directing to the index and the other dev's new guidelines. The index has maintenance rules baked in — when files are added, moved, or deleted, the corresponding table row must be updated.

What's Next

• Character creation, title screen, and machining skill are merged and working — ready for the other dev to build on
• Test suite runs in under 300ms and should be part of every push workflow
• Codebase index needs to stay current as both devs continue adding systems
• The test infrastructure is ready for expansion: crafting validation, spell scaling, job prerequisite checks