test: Add comprehensive tests for memoryStats function

Adds `test/memory-stats.test.mjs` to validats `memoryStats` behavior including:
- Empty and populated repository states
- Ingest throughput calculation with mocked time
- Deleted rate metrics
- Window parameter handling

Co-authored-by: PR0M3TH3AN <[email protected]>

test/memory-stats.test.mjs

@@ -0,0 +1,138 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import {
+  memoryStats,
+  ingestEvents,
+  runPruneCycle,
+} from '../src/services/memory/index.js';
+
+test('memoryStats with empty repository returns zero counts and rates', async () => {
+  const repository = {
+    async listMemories() {
+      return [];
+    },
+  };
+  const stats = await memoryStats({ repository });
+
+  assert.deepEqual(stats.countsByType, {});
+  assert.equal(stats.totals.total, 0);
+  assert.equal(stats.totals.pinned, 0);
+  assert.equal(stats.totals.archived, 0);
+  assert.equal(stats.rates.archivedRate, 0);
+  assert.ok(Number.isFinite(stats.rates.deletedRate));
+  assert.equal(stats.indexSizeEstimateBytes, 0);
+  assert.ok(Number.isFinite(stats.ingestThroughputPerMinute));
+});
+
+test('memoryStats with populated repository returns correct counts and totals', async () => {
+  const memories = [
+    { type: 'event', pinned: false, merged_into: null },
+    { type: 'event', pinned: true, merged_into: null },
+    { type: 'summary', pinned: false, merged_into: 'some-id' },
+  ];
+  const repository = {
+    async listMemories() {
+      return memories;
+    },
+  };
+
+  const stats = await memoryStats({ repository });
+
+  assert.equal(stats.countsByType.event, 2);
+  assert.equal(stats.countsByType.summary, 1);
+  assert.equal(stats.totals.total, 3);
+  assert.equal(stats.totals.pinned, 1);
+  assert.equal(stats.totals.archived, 1);
+
+  // archivedRate = archived / max(1, total) = 1 / 3
+  assert.equal(stats.rates.archivedRate, 1 / 3);
+
+  // indexSizeEstimateBytes = 3 * 512 = 1536
+  assert.equal(stats.indexSizeEstimateBytes, 1536);
+});
+
+test('memoryStats calculates ingest throughput based on window', async (t) => {
+  t.mock.timers.enable({ apis: ['Date'] });
+  const baseTime = 1000000;
+  t.mock.timers.setTime(baseTime);
+
+  const repository = {
+    async insertMemory() { return {}; },
+    async hasIngestionFingerprint() { return false; },
+    async storeIngestionFingerprint() { },
+    async linkEmbedding() { },
+    async listMemories() { return []; },
+  };
+
+  // Create 3 distinct records (different agents to avoid batching into one record)
+  await ingestEvents([
+    { content: 'e1', agent_id: 'agent-1', timestamp: baseTime },
+    { content: 'e2', agent_id: 'agent-2', timestamp: baseTime },
+    { content: 'e3', agent_id: 'agent-3', timestamp: baseTime },
+  ], { repository });
+
+  // Move time forward 30 mins
+  const checkTime = baseTime + 30 * 60 * 1000;
+  t.mock.timers.setTime(checkTime);
+
+  // Check stats with 60 min window (should include baseTime)
+  // Window: [checkTime - 60min, checkTime] = [baseTime - 30min, baseTime + 30min]
+  const stats1 = await memoryStats({
+    repository,
+    now: checkTime,
+    windowMs: 60 * 60 * 1000
+  });
+
+  // We expect 3 ingested items in this window.
+  // throughput = 3 / (60 mins) = 0.05
+  assert.equal(stats1.ingestThroughputPerMinute, 3 / 60);
+
+  // Check stats with window that excludes the events (checkTime + 90 mins)
+  const farTime = baseTime + 90 * 60 * 1000;
+  // Window: [farTime - 60min, farTime] = [baseTime + 30min, baseTime + 90min]
+  // Events at baseTime are < baseTime + 30min, so excluded.
+
+  const stats2 = await memoryStats({
+    repository,
+    now: farTime,
+    windowMs: 60 * 60 * 1000
+  });
+
+  assert.equal(stats2.ingestThroughputPerMinute, 0);
+});
+
+test('memoryStats reflects deleted count from prune cycle', async () => {
+  const repository = {
+    async listPruneCandidates() {
+      // Return 2 candidates to be pruned
+      return [
+         { id: 'p1', agent_id: 'a', type: 'event', last_seen: 0, pinned: false },
+         { id: 'p2', agent_id: 'a', type: 'event', last_seen: 0, pinned: false },
+      ];
+    },
+    async listMemories() { return []; }
+  };
+
+  // Run prune cycle
+  await runPruneCycle({ repository, retentionMs: 100, now: 1000 });
+
+  const stats = await memoryStats({ repository });
+
+  // deletedObserved should be increased by 2.
+  assert.ok(stats.totals.deletedObserved >= 2);
+
+  // deletedRate should be > 0.
+  assert.ok(stats.rates.deletedRate > 0);
+});
+
+test('memoryStats handles windowMs parameter correctly', async () => {
+  const repository = { async listMemories() { return []; } };
+
+  // Test with invalid windowMs, should default to 1 hour (60 mins)
+  const statsDefault = await memoryStats({ repository, windowMs: 'invalid' });
+  assert.ok(Number.isFinite(statsDefault.ingestThroughputPerMinute));
+
+  // Test with very small window
+  const statsSmall = await memoryStats({ repository, windowMs: 1 });
+  assert.ok(Number.isFinite(statsSmall.ingestThroughputPerMinute));
+});