diff --git a/server/src/engine/answers.test.ts b/server/src/engine/answers.test.ts
index 46ef785..a413b53 100644
--- a/server/src/engine/answers.test.ts
+++ b/server/src/engine/answers.test.ts
@@ -120,4 +120,28 @@ describe('checkAnswer', () => {
     // 'a' length is 1, so containment shouldn't trigger (requires >= 2)
     expect(score).toBeLessThanOrEqual(0.8)
   })
+
+  it('special characters in answer', () => {
+    expect(checkAnswer('C++', ['C++'])).toBe(1.0)
+    expect(checkAnswer('c++', ['C++'])).toBe(1.0)
+    expect(checkAnswer('$100', ['$100'])).toBe(1.0)
+    expect(checkAnswer('42%', ['42'])).toBe(1.0)
+  })
+
+  it('very long answer still matches if correct keyword present', () => {
+    const longAnswer = 'Well, after much deliberation and careful consideration of all the facts, ' +
+      'weighing the evidence both for and against, consulting multiple sources, and thinking deeply ' +
+      'about the philosophical implications, I believe the answer you are looking for is Paris, ' +
+      'which is of course the beautiful capital of France.'
+    expect(checkAnswer(longAnswer, ['Paris'])).toBe(1.0)
+  })
+
+  it('very long answer with no match returns 0', () => {
+    const longWrong = 'A'.repeat(2000) + ' banana ' + 'B'.repeat(2000)
+    expect(checkAnswer(longWrong, ['Paris'])).toBe(0)
+  })
+
+  it('whitespace-only answer returns 0', () => {
+    expect(checkAnswer('\t\n  \r', ['Paris'])).toBe(0)
+  })
 })
diff --git a/server/src/engine/challenges.test.ts b/server/src/engine/challenges.test.ts
index a7b2531..11c8463 100644
--- a/server/src/engine/challenges.test.ts
+++ b/server/src/engine/challenges.test.ts
@@ -1,5 +1,5 @@
 import { describe, it, expect } from 'vitest'
-import { pickChallenge, getAllChallengeTypes, getAnswerPool } from './challenges.js'
+import { pickChallenge, pickRankedChallenge, getAllChallengeTypes, getAnswerPool } from './challenges.js'
 
 describe('pickChallenge', () => {
   it('returns a valid challenge', () => {
@@ -66,6 +66,64 @@ describe('pickChallenge', () => {
     // With 50 tries, choices should appear in more than one order
     expect(orders.size).toBeGreaterThan(1)
   })
+
+  it('distribution: ~70% factual, ~30% creative over many picks', () => {
+    let factual = 0
+    let creative = 0
+    const runs = 1000
+    for (let i = 0; i < runs; i++) {
+      const c = pickChallenge(new Set(), null)
+      if (c.scoring === 'factual') factual++
+      else creative++
+    }
+    const factualPct = factual / runs
+    // Allow ±10% tolerance due to randomness
+    expect(factualPct).toBeGreaterThan(0.55)
+    expect(factualPct).toBeLessThan(0.85)
+  })
+
+  it('True/False auto-generation for boolean answers', () => {
+    // Pick many challenges, find ones with answers = ['true'] or ['false']
+    let foundTFWithChoices = false
+    for (let i = 0; i < 500; i++) {
+      const c = pickChallenge(new Set(), null)
+      if (c.answers?.length === 1 && ['true', 'false'].includes(c.answers[0].toLowerCase())) {
+        expect(c.choices).toBeTruthy()
+        expect(c.choices!.length).toBe(2)
+        expect(c.choices!.sort()).toEqual(['False', 'True'])
+        foundTFWithChoices = true
+      }
+    }
+    expect(foundTFWithChoices).toBe(true)
+  })
+})
+
+describe('pickRankedChallenge', () => {
+  it('never returns choices', () => {
+    for (let i = 0; i < 100; i++) {
+      const c = pickRankedChallenge(new Set())
+      expect(c.choices).toBeUndefined()
+    }
+  })
+
+  it('returns valid challenge structure', () => {
+    const c = pickRankedChallenge(new Set())
+    expect(c.type).toBeTruthy()
+    expect(c.prompt).toBeTruthy()
+    expect(c.timeout_ms).toBeGreaterThan(0)
+    expect(c.baseDamage).toBeGreaterThan(0)
+  })
+
+  it('avoids used types', () => {
+    const types = getAllChallengeTypes()
+    const used = new Set(types.slice(0, -1))
+    let gotRemaining = false
+    for (let i = 0; i < 50; i++) {
+      const c = pickRankedChallenge(used)
+      if (c.type === types[types.length - 1]) gotRemaining = true
+    }
+    expect(gotRemaining).toBe(true)
+  })
 })
 
 describe('getAllChallengeTypes', () => {
diff --git a/server/src/engine/mock.test.ts b/server/src/engine/mock.test.ts
index 79f34b2..bb55711 100644
--- a/server/src/engine/mock.test.ts
+++ b/server/src/engine/mock.test.ts
@@ -1,6 +1,6 @@
 import { describe, it, expect } from 'vitest'
 import { mockResponse } from './mock.js'
-import { pickChallenge } from './challenges.js'
+import { pickChallenge, getAllChallengeTypes } from './challenges.js'
 
 describe('mockResponse', () => {
   it('returns a valid response structure', () => {
@@ -101,4 +101,47 @@ describe('mockResponse', () => {
       expect(resp.timeMs).toBeGreaterThan(0)
     }
   })
+
+  it('produces valid responses for all 16 challenge types', () => {
+    const types = getAllChallengeTypes()
+    expect(types.length).toBe(16)
+
+    for (const type of types) {
+      // Force pick a challenge of this type by using all other types
+      const otherTypes = new Set(types.filter(t => t !== type))
+      const challenge = pickChallenge(otherTypes, null)
+      // May not get exact type if creative/factual split causes fallback, but should still work
+      const resp = mockResponse(challenge, 'confident', 1500)
+      expect(resp).toHaveProperty('answer')
+      expect(resp).toHaveProperty('timeMs')
+      expect(resp.timeMs).toBeGreaterThan(0)
+    }
+  })
+
+  it('answer is empty string on timeout', () => {
+    // Run many times with very low elo to trigger timeouts
+    let foundTimeout = false
+    for (let i = 0; i < 200; i++) {
+      const challenge = pickChallenge(new Set(), null)
+      const resp = mockResponse(challenge, 'clueless', 500)
+      if (resp.timedOut) {
+        expect(resp.answer).toBe('')
+        foundTimeout = true
+      }
+    }
+    expect(foundTimeout).toBe(true)
+  })
+
+  it('answer is empty string on error', () => {
+    let foundError = false
+    for (let i = 0; i < 200; i++) {
+      const challenge = pickChallenge(new Set(), null)
+      const resp = mockResponse(challenge, 'clueless', 500)
+      if (resp.error) {
+        expect(resp.answer).toBe('')
+        foundError = true
+      }
+    }
+    expect(foundError).toBe(true)
+  })
 })