diff --git a/tests/game-logic.test.mjs b/tests/game-logic.test.mjs
new file mode 100644
index 0000000..d0ec1c0
--- /dev/null
+++ b/tests/game-logic.test.mjs
@@ -0,0 +1,109 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+
+import {
+  DEFAULT_PIRATE_SHOT_DAMAGE,
+  PLAYER_HIT_COOLDOWN_MS,
+  PLAYER_MAX_HULL,
+  normalizePlayerDamage,
+  reducePlayerHitQueue,
+} from '../src/game-logic.js';
+
+test('first pirate hit removes exactly the default damage and does not end the game', () => {
+  const result = reducePlayerHitQueue({
+    hull: PLAYER_MAX_HULL,
+    lastHitAt: -Infinity,
+    now: 1000,
+    damages: [DEFAULT_PIRATE_SHOT_DAMAGE],
+  });
+
+  assert.equal(result.hull, 94);
+  assert.equal(result.appliedHits, 1);
+  assert.equal(result.ignoredHits, 0);
+  assert.equal(result.totalDamage, 6);
+  assert.equal(result.gameOver, false);
+});
+
+test('three cannonballs arriving in one broadside only apply one hull hit', () => {
+  const result = reducePlayerHitQueue({
+    hull: 100,
+    lastHitAt: -Infinity,
+    now: 2000,
+    damages: [6, 6, 6],
+  });
+
+  assert.equal(result.hull, 94);
+  assert.equal(result.appliedHits, 1);
+  assert.equal(result.ignoredHits, 2);
+});
+
+test('hit inside cooldown is ignored and exact cooldown boundary is accepted', () => {
+  const blocked = reducePlayerHitQueue({
+    hull: 94,
+    lastHitAt: 1000,
+    now: 1000 + PLAYER_HIT_COOLDOWN_MS - 1,
+    damages: [6],
+  });
+
+  assert.equal(blocked.hull, 94);
+  assert.equal(blocked.appliedHits, 0);
+  assert.equal(blocked.ignoredHits, 1);
+
+  const accepted = reducePlayerHitQueue({
+    hull: 94,
+    lastHitAt: 1000,
+    now: 1000 + PLAYER_HIT_COOLDOWN_MS,
+    damages: [6],
+  });
+
+  assert.equal(accepted.hull, 88);
+  assert.equal(accepted.appliedHits, 1);
+});
+
+test('damage normalization handles invalid and extreme values safely', () => {
+  assert.equal(normalizePlayerDamage(undefined), 6);
+  assert.equal(normalizePlayerDamage('not-a-number'), 6);
+  assert.equal(normalizePlayerDamage(999), 25);
+  assert.equal(normalizePlayerDamage(-12), 1);
+  assert.equal(normalizePlayerDamage('8'), 8);
+});
+
+test('invalid hull state recovers from max hull before applying damage', () => {
+  const result = reducePlayerHitQueue({
+    hull: Number.NaN,
+    lastHitAt: -Infinity,
+    now: 3000,
+    damages: [6],
+  });
+
+  assert.equal(result.hull, 94);
+  assert.equal(result.gameOver, false);
+});
+
+test('lethal hit clamps hull at zero and reports game over', () => {
+  const result = reducePlayerHitQueue({
+    hull: 5,
+    lastHitAt: -Infinity,
+    now: 4000,
+    damages: [6],
+  });
+
+  assert.equal(result.hull, 0);
+  assert.equal(result.totalDamage, 6);
+  assert.equal(result.gameOver, true);
+});
+
+test('empty hit queue is a no-op', () => {
+  const result = reducePlayerHitQueue({
+    hull: 72,
+    lastHitAt: 1234,
+    now: 5000,
+    damages: [],
+  });
+
+  assert.equal(result.hull, 72);
+  assert.equal(result.lastHitAt, 1234);
+  assert.equal(result.appliedHits, 0);
+  assert.equal(result.ignoredHits, 0);
+  assert.equal(result.gameOver, false);
+});