diff --git a/packages/pokemon/src/__tests__/battle.test.ts b/packages/pokemon/src/__tests__/battle.test.ts
new file mode 100644
index 000000000..51b825f4f
--- /dev/null
+++ b/packages/pokemon/src/__tests__/battle.test.ts
@@ -0,0 +1,232 @@
+import { describe, test, expect } from 'bun:test'
+import { createBattle, executeTurn } from '../battle/engine'
+import { settleBattle, applyMoveLearn, applyEvolution } from '../battle/settlement'
+import { chooseAIMove } from '../battle/ai'
+import type { Creature, BuddyData } from '../types'
+
+function makeTestCreature(overrides: Partial<Creature> = {}): Creature {
+	return {
+		id: overrides.id ?? 'test-1',
+		speciesId: overrides.speciesId ?? 'charmander',
+		gender: overrides.gender ?? 'male',
+		level: overrides.level ?? 50,
+		xp: 0,
+		totalXp: 0,
+		nature: overrides.nature ?? 'adamant',
+		ev: overrides.ev ?? { hp: 0, attack: 0, defense: 0, spAtk: 0, spDef: 0, speed: 0 },
+		iv: overrides.iv ?? { hp: 31, attack: 31, defense: 31, spAtk: 31, spDef: 31, speed: 31 },
+		moves: overrides.moves ?? [
+			{ id: 'flamethrower', pp: 15, maxPp: 15 },
+			{ id: 'airslash', pp: 15, maxPp: 15 },
+			{ id: 'dragontail', pp: 10, maxPp: 10 },
+			{ id: 'slash', pp: 20, maxPp: 20 },
+		],
+		ability: overrides.ability ?? 'blaze',
+		heldItem: null,
+		friendship: 70,
+		isShiny: false,
+		hatchedAt: Date.now(),
+		pokeball: 'pokeball',
+	}
+}
+
+function makeTestBuddyData(creatures: Creature[] = [makeTestCreature()]): BuddyData {
+	return {
+		version: 2,
+		party: [creatures[0]!.id, null, null, null, null, null],
+		boxes: [],
+		creatures: creatures,
+		eggs: [],
+		dex: [],
+		bag: { items: [] },
+		stats: {
+			totalTurns: 0,
+			consecutiveDays: 0,
+			lastActiveDate: '',
+			totalEggsObtained: 0,
+			totalEvolutions: 0,
+			battlesWon: 0,
+			battlesLost: 0,
+		},
+	}
+}
+
+describe('createBattle', () => {
+	test('creates battle with valid initial state', () => {
+		const creature = makeTestCreature()
+		const init = createBattle([creature], 'squirtle', 50)
+		expect(init.state).toBeDefined()
+		expect(init.state.playerPokemon).toBeDefined()
+		expect(init.state.opponentPokemon).toBeDefined()
+		expect(init.state.finished).toBe(false)
+	})
+
+	test('player pokemon has correct species', () => {
+		const creature = makeTestCreature()
+		const init = createBattle([creature], 'bulbasaur', 30)
+		expect(init.state.playerPokemon.speciesId).toBe('charmander')
+		expect(init.state.opponentPokemon.speciesId).toBe('bulbasaur')
+	})
+
+	test('player pokemon has moves', () => {
+		const creature = makeTestCreature()
+		const init = createBattle([creature], 'squirtle', 50)
+		expect(init.state.playerPokemon.moves.length).toBeGreaterThan(0)
+	})
+})
+
+describe('executeTurn', () => {
+	test('move action generates events', () => {
+		const creature = makeTestCreature()
+		const init = createBattle([creature], 'squirtle', 50)
+		const initialEventCount = init.state.events.length
+
+		const newState = executeTurn(init, { type: 'move', moveIndex: 0 })
+		expect(newState.events.length).toBeGreaterThanOrEqual(initialEventCount)
+	})
+
+	test('battle eventually ends within 50 turns', () => {
+		const creature = makeTestCreature({ level: 100, ev: { hp: 252, attack: 252, defense: 0, spAtk: 0, spDef: 0, speed: 252 } })
+		const init = createBattle([creature], 'squirtle', 5)
+
+		let state = init.state
+		for (let i = 0; i < 50 && !state.finished; i++) {
+			state = executeTurn(init, { type: 'move', moveIndex: 0 })
+		}
+
+		expect(state.finished).toBe(true)
+	})
+})
+
+describe('settleBattle', () => {
+	test('player win increments battlesWon', () => {
+		const creature = makeTestCreature()
+		const data: BuddyData = {
+			version: 2,
+			party: [creature.id, null, null, null, null, null],
+			boxes: [],
+			creatures: [creature],
+			eggs: [],
+			dex: [],
+			bag: { items: [] },
+			stats: {
+				totalTurns: 0,
+				consecutiveDays: 0,
+				lastActiveDate: '',
+				totalEggsObtained: 0,
+				totalEvolutions: 0,
+				battlesWon: 0,
+				battlesLost: 0,
+			},
+		}
+		const result = {
+			winner: 'player' as const,
+			turns: 5,
+			xpGained: 0,
+			evGained: { hp: 0, attack: 0, defense: 0, spAtk: 0, spDef: 0, speed: 0 },
+			participantIds: [creature.id],
+		}
+
+		const settlement = settleBattle(data, result, 'squirtle', 20)
+		expect(settlement.data.stats.battlesWon).toBe(1)
+	})
+
+	test('player loss returns unchanged data', () => {
+		const creature = makeTestCreature()
+		const data: BuddyData = {
+			version: 2,
+			party: [creature.id, null, null, null, null, null],
+			boxes: [],
+			creatures: [creature],
+			eggs: [],
+			dex: [],
+			bag: { items: [] },
+			stats: {
+				totalTurns: 0,
+				consecutiveDays: 0,
+				lastActiveDate: '',
+				totalEggsObtained: 0,
+				totalEvolutions: 0,
+				battlesWon: 0,
+				battlesLost: 0,
+			},
+		}
+		const result = {
+			winner: 'opponent' as const,
+			turns: 3,
+			xpGained: 0,
+			evGained: { hp: 0, attack: 0, defense: 0, spAtk: 0, spDef: 0, speed: 0 },
+			participantIds: [creature.id],
+		}
+
+		const settlement = settleBattle(data, result, 'squirtle', 20)
+		// Loss early-returns unchanged data
+		expect(settlement.data.creatures[0]!.totalXp).toBe(creature.totalXp)
+		expect(settlement.learnableMoves).toEqual([])
+		expect(settlement.pendingEvolutions).toEqual([])
+	})
+})
+
+describe('applyMoveLearn', () => {
+	test('replaces move at given index', () => {
+		const creature = makeTestCreature()
+		const data: BuddyData = {
+			version: 2,
+			party: [creature.id, null, null, null, null, null],
+			boxes: [],
+			creatures: [creature],
+			eggs: [],
+			dex: [],
+			bag: { items: [] },
+			stats: {
+				totalTurns: 0,
+				consecutiveDays: 0,
+				lastActiveDate: '',
+				totalEggsObtained: 0,
+				totalEvolutions: 0,
+				battlesWon: 0,
+				battlesLost: 0,
+			},
+		}
+		const updated = applyMoveLearn(data, creature.id, 'fireblast', 3)
+		expect(updated.creatures[0]!.moves[3]!.id).toBe('fireblast')
+	})
+})
+
+describe('applyEvolution', () => {
+	test('evolves charmander to charmeleon and increments counter', () => {
+		const creature = makeTestCreature({ speciesId: 'charmander' })
+		const data: BuddyData = {
+			version: 2,
+			party: [creature.id, null, null, null, null, null],
+			boxes: [],
+			creatures: [creature],
+			eggs: [],
+			dex: [],
+			bag: { items: [] },
+			stats: {
+				totalTurns: 0,
+				consecutiveDays: 0,
+				lastActiveDate: '',
+				totalEggsObtained: 0,
+				totalEvolutions: 0,
+				battlesWon: 0,
+				battlesLost: 0,
+			},
+		}
+		const updated = applyEvolution(data, creature.id, 'charmeleon')
+		expect(updated.creatures[0]!.speciesId).toBe('charmeleon')
+		expect(updated.stats.totalEvolutions).toBe(1)
+	})
+})
+
+describe('chooseAIMove', () => {
+	test('returns a valid move index', () => {
+		const creature = makeTestCreature()
+		const init = createBattle([creature], 'squirtle', 50)
+		const aiPokemon = init.state.opponentPokemon
+		const idx = chooseAIMove(aiPokemon)
+		expect(idx).toBeGreaterThanOrEqual(0)
+		expect(idx).toBeLessThan(aiPokemon.moves.length)
+	})
+})
diff --git a/packages/pokemon/src/__tests__/egg.test.ts b/packages/pokemon/src/__tests__/egg.test.ts
index f24567ccf..723fefe02 100644
--- a/packages/pokemon/src/__tests__/egg.test.ts
+++ b/packages/pokemon/src/__tests__/egg.test.ts
@@ -62,7 +62,7 @@ describe('checkEggEligibility', () => {
 	})
 
 	test('not eligible with low consecutive days', () => {
-		const data = makeBuddyData({ consecutiveDays: 3 })
+		const data = makeBuddyData({ consecutiveDays: 2 })
 		expect(checkEggEligibility(data)).toBe(false)
 	})
 
diff --git a/packages/pokemon/src/__tests__/learnsets.test.ts b/packages/pokemon/src/__tests__/learnsets.test.ts
new file mode 100644
index 000000000..8888cd642
--- /dev/null
+++ b/packages/pokemon/src/__tests__/learnsets.test.ts
@@ -0,0 +1,59 @@
+import { describe, test, expect } from 'bun:test'
+import { getDefaultMoveset, getDefaultAbility, getNewLearnableMoves } from '../data/learnsets'
+import { EMPTY_MOVE } from '../types'
+
+describe('getDefaultMoveset', () => {
+	test('charmander at level 1 has at least one move', async () => {
+		const moves = await getDefaultMoveset('charmander', 1)
+		expect(moves.length).toBe(4)
+		expect(moves[0]!.id).not.toBe('')
+	})
+
+	test('charmander at level 10 has more moves', async () => {
+		const moves = await getDefaultMoveset('charmander', 10)
+		const nonEmpty = moves.filter(m => m.id !== '')
+		expect(nonEmpty.length).toBeGreaterThan(1)
+	})
+
+	test('all moves have valid pp', async () => {
+		const moves = await getDefaultMoveset('bulbasaur', 20)
+		for (const move of moves) {
+			if (move.id) {
+				expect(move.pp).toBeGreaterThan(0)
+				expect(move.maxPp).toBeGreaterThan(0)
+			}
+		}
+	})
+
+	test('invalid species returns empty moves', async () => {
+		const moves = await getDefaultMoveset('nonexistent' as any, 10)
+		expect(moves.every(m => m.id === '')).toBe(true)
+	})
+})
+
+describe('getDefaultAbility', () => {
+	test('charmander has blaze', () => {
+		expect(getDefaultAbility('charmander')).toBe('blaze')
+	})
+
+	test('bulbasaur has overgrow', () => {
+		expect(getDefaultAbility('bulbasaur')).toBe('overgrow')
+	})
+
+	test('squirtle has torrent', () => {
+		expect(getDefaultAbility('squirtle')).toBe('torrent')
+	})
+})
+
+describe('getNewLearnableMoves', () => {
+	test('charmander gains ember at level 4', async () => {
+		const moves = await getNewLearnableMoves('charmander', 1, 4)
+		expect(moves.length).toBeGreaterThan(0)
+		expect(moves.some(m => m.id === 'ember')).toBe(true)
+	})
+
+	test('no new moves when level stays same', async () => {
+		const moves = await getNewLearnableMoves('charmander', 5, 5)
+		expect(moves.length).toBe(0)
+	})
+})
diff --git a/packages/pokemon/src/__tests__/nature.test.ts b/packages/pokemon/src/__tests__/nature.test.ts
new file mode 100644
index 000000000..f22482f09
--- /dev/null
+++ b/packages/pokemon/src/__tests__/nature.test.ts
@@ -0,0 +1,53 @@
+import { describe, test, expect } from 'bun:test'
+import { getAllNatureNames, randomNature, getNatureEffect } from '../data/nature'
+
+describe('getAllNatureNames', () => {
+	test('returns 25 nature names', () => {
+		const names = getAllNatureNames()
+		expect(names.length).toBe(25)
+	})
+
+	test('includes hardy and quirky', () => {
+		const names = getAllNatureNames()
+		expect(names).toContain('hardy')
+		expect(names).toContain('quirky')
+	})
+})
+
+describe('randomNature', () => {
+	test('returns a valid nature name', () => {
+		const nature = randomNature()
+		expect(getAllNatureNames()).toContain(nature)
+	})
+
+	test('produces different natures over multiple calls', () => {
+		const natures = new Set(Array.from({ length: 50 }, () => randomNature()))
+		expect(natures.size).toBeGreaterThan(1)
+	})
+})
+
+describe('getNatureEffect', () => {
+	test('hardy is neutral (no effect)', () => {
+		const effect = getNatureEffect('hardy')
+		expect(effect.plus).toBeNull()
+		expect(effect.minus).toBeNull()
+	})
+
+	test('adamant boosts attack and lowers spAtk', () => {
+		const effect = getNatureEffect('adamant')
+		expect(effect.plus).toBe('attack')
+		expect(effect.minus).toBe('spAtk')
+	})
+
+	test('timid boosts speed and lowers attack', () => {
+		const effect = getNatureEffect('timid')
+		expect(effect.plus).toBe('speed')
+		expect(effect.minus).toBe('attack')
+	})
+
+	test('invalid nature returns neutral', () => {
+		const effect = getNatureEffect('nonexistent')
+		expect(effect.plus).toBeNull()
+		expect(effect.minus).toBeNull()
+	})
+})
diff --git a/packages/pokemon/src/__tests__/storage.test.ts b/packages/pokemon/src/__tests__/storage.test.ts
new file mode 100644
index 000000000..6df65a716
--- /dev/null
+++ b/packages/pokemon/src/__tests__/storage.test.ts
@@ -0,0 +1,32 @@
+import { describe, test, expect } from 'bun:test'
+import { getDefaultBuddyData } from '../core/storage'
+
+describe('getDefaultBuddyData', () => {
+	test('returns v2 data with correct structure', async () => {
+		const data = await getDefaultBuddyData()
+		expect(data.version).toBe(2)
+		expect(data.party.length).toBe(6)
+		expect(data.party[0]).toBeTruthy()
+		expect(data.boxes.length).toBe(8)
+		expect(data.boxes[0]!.slots.length).toBe(30)
+		expect(data.bag.items).toEqual([])
+		expect(data.stats.battlesWon).toBe(0)
+		expect(data.stats.battlesLost).toBe(0)
+	})
+
+	test('has one creature matching party[0]', async () => {
+		const data = await getDefaultBuddyData()
+		expect(data.creatures.length).toBe(1)
+		expect(data.creatures[0]!.id).toBe(data.party[0]!)
+	})
+
+	test('creature has v2 fields', async () => {
+		const data = await getDefaultBuddyData()
+		const creature = data.creatures[0]!
+		expect(creature.nature).toBeTruthy()
+		expect(creature.moves.length).toBe(4)
+		expect(creature.ability).toBeTruthy()
+		expect(creature.heldItem).toBeNull()
+		expect(creature.pokeball).toBe('pokeball')
+	})
+})
diff --git a/packages/pokemon/src/data/nature.ts b/packages/pokemon/src/data/nature.ts
index 7bc408c91..c79234504 100644
--- a/packages/pokemon/src/data/nature.ts
+++ b/packages/pokemon/src/data/nature.ts
@@ -1,4 +1,5 @@
 import { Dex } from '@pkmn/sim'
+import { FROM_DEX_STAT } from './pkmn'
 import type { NatureName, NatureEffect, NatureStat } from '../types'
 
 // All 25 canonical nature names (Dex.natures is not iterable, so we list them)
@@ -21,12 +22,18 @@ export function randomNature(): NatureName {
 	return names[Math.floor(Math.random() * names.length)]!
 }
 
+/** Map Dex stat abbreviation (atk, spa, spe, etc.) to our NatureStat format */
+function mapDexStat(stat: string | undefined): NatureStat | null {
+	if (!stat) return null
+	return (FROM_DEX_STAT[stat] as NatureStat) ?? null
+}
+
 /** Get nature effect (plus/minus stat, or null for neutral) — delegates to Dex.natures */
 export function getNatureEffect(nature: NatureName): NatureEffect {
 	const n = Dex.natures.get(nature)
 	if (!n?.exists) return { plus: null, minus: null }
 	return {
-		plus: (n.plus as NatureStat | undefined) ?? null,
-		minus: (n.minus as NatureStat | undefined) ?? null,
+		plus: mapDexStat(n.plus),
+		minus: mapDexStat(n.minus),
 	}
 }