Refactor topic metadata: cut CRAP, share test doubles, harden property tests

- Replace the ternary follower delta in recordTopicFollow with
  Number(isActive) - Number(wasActive), dropping its cyclomatic complexity
  from 8 to 6 (CRAP 8.0 -> 6.0). No behavior change.
- Extend the indexer topic property test to conserve lastSeen (newest post
  time) and followerCount (each address's final active follow state)
  alongside postCount/lastHeight, with varying post seen times.
- Extend the DB backfill and topic-query property tests to conserve lastSeen
  and followerCount; generated follows now include unfollows.
- Add a client topic-metadata property test covering relativeTime bucket
  classification, pluralization, monotonicity, and getLastSeenLabel
  consistency, and cover ensureTopicRoom's existing-summary path plus
  recordTopicFollow's legacy-follower-count fallback.
- Share one in-memory DB double per component (indexer test/support/
  memory-db.js, DB test/support/level-double.js) and table-drive the
  parallel topic-follow/topic-message/topic-query cases, clearing every
  dry4javascript candidate in the changed files.

Verification: indexer 113 unit / 12 property / 7 acceptance; db 387 unit /
57 property / 16 acceptance; client 441 unit / 90 property / 33 acceptance
+ build; lint clean. CRAP max 6.0; mutation scans under 100 sites/file.

By refactorer.

psf-memo-client/test/property/topic-metadata.property.test.js

@@ -0,0 +1,121 @@
+/*
+  Property tests for the topic metadata display helpers.
+
+  The unit tests probe relativeTime and getLastSeenLabel at fixed fixtures.
+  These properties pin down the formatting contract over broad random times:
+
+    - Classification: the label matches the feature spec's buckets computed
+      independently from elapsed time.
+    - Pluralization: a label is singular exactly when its magnitude is one.
+    - Monotonicity: a longer elapsed time never yields a smaller hour/day
+      magnitude, so the label orders time correctly.
+    - Consistency: getLastSeenLabel returns the same label relativeTime
+      produces for a loaded topic, and null for an unknown topic.
+
+  `now` is injected so every property is deterministic.
+*/
+
+'use strict'
+
+const test = require('node:test')
+const assert = require('node:assert/strict')
+const { seededRandom, forAll, intGen } = require('./harness')
+const { relativeTime } = require('../../src/services/relative-time')
+const TopicDiscoveryPage = require('../../src/services/topic-discovery-page')
+
+const rng = seededRandom(20260918)
+
+const HOUR = 60 * 60 * 1000
+const DAY = 24 * HOUR
+const NOW = 1800000000000
+
+// Reference classifier written from the feature spec, independent of the
+// implementation under test.
+function expectedLabel (elapsed) {
+  if (elapsed < HOUR) return 'Less than an hour ago'
+  if (elapsed < DAY) {
+    const hours = Math.floor(elapsed / HOUR)
+    return hours === 1 ? '1 hour ago' : `${hours} hours ago`
+  }
+  const days = Math.floor(elapsed / DAY)
+  return days === 1 ? '1 day ago' : `${days} days ago`
+}
+
+// Convert an hour/day label back to a magnitude in hours, for ordering checks.
+function elapsedHours (label) {
+  const match = /^(\d+) (hour|day)s? ago$/.exec(label)
+  if (!match) return 0
+  const value = Number(match[1])
+  return match[2] === 'day' ? value * 24 : value
+}
+
+test('relativeTime classifies every elapsed time per the spec buckets', async () => {
+  await forAll(
+    () => intGen(rng, 0, 400 * DAY)(),
+    (elapsed) => relativeTime(NOW - elapsed, NOW) === expectedLabel(elapsed),
+    { label: 'relativeTime bucket classification' }
+  )
+})
+
+test('relativeTime labels are singular exactly at magnitude one', async () => {
+  await forAll(
+    () => intGen(rng, HOUR, 365 * DAY)(),
+    (elapsed) => {
+      const label = relativeTime(NOW - elapsed, NOW)
+      const match = /^(\d+) (hour|day)s? ago$/.exec(label)
+      if (!match) return false
+      return label.includes('s ago') === (Number(match[1]) !== 1)
+    },
+    { label: 'relativeTime pluralization' }
+  )
+})
+
+test('relativeTime is monotonic as elapsed time grows', async () => {
+  await forAll(
+    () => {
+      const first = HOUR + intGen(rng, 0, 60 * DAY)()
+      return { first, second: first + intGen(rng, 0, 60 * DAY)() }
+    },
+    ({ first, second }) => {
+      return elapsedHours(relativeTime(NOW - first, NOW)) <=
+        elapsedHours(relativeTime(NOW - second, NOW))
+    },
+    { label: 'relativeTime monotonicity' }
+  )
+})
+
+test('relativeTime reports "No posts" for a missing last-seen time', () => {
+  for (const lastSeen of [0, null, undefined]) {
+    assert.equal(relativeTime(lastSeen, NOW), 'No posts')
+  }
+})
+
+test('getLastSeenLabel mirrors relativeTime for loaded topics and null otherwise', async () => {
+  await forAll(
+    () => {
+      const topics = []
+      const count = intGen(rng, 0, 10)()
+      for (let i = 0; i < count; i++) {
+        topics.push({
+          room: `room-${i}`,
+          postCount: 1,
+          lastSeen: NOW - intGen(rng, 0, 400 * DAY)()
+        })
+      }
+      return topics
+    },
+    async (topics) => {
+      const page = new TopicDiscoveryPage({
+        memoDb: { async getTopics () { return { topics } } }
+      })
+      await page.load()
+
+      for (const topic of topics) {
+        if (page.getLastSeenLabel(topic.room, NOW) !== relativeTime(topic.lastSeen, NOW)) return false
+      }
+      if (page.getLastSeenLabel('missing-room', NOW) !== null) return false
+      return true
+    },
+    { label: 'getLastSeenLabel consistency' }
+  )
+})

psf-memo-client/test/unit/topic-discovery-page.test.js

@@ -19,6 +19,13 @@ function makeMemoDb ({ topics = [], pagination = null } = {}) {
   }
 }
 
+// Build a controller over a fixed topic list and run its initial load.
+async function loadPage (topics) {
+  const page = new TopicDiscoveryPage({ memoDb: makeMemoDb({ topics }) })
+  await page.load()
+  return page
+}
+
 test('load returns topics with post counts', async () => {
   const topics = [
     { room: 'bitcoin', postCount: 2 },
@@ -95,45 +102,31 @@ test('getTopic returns the matching topic', async () => {
     { room: 'bitcoin', postCount: 2 },
     { room: 'cash', postCount: 1 }
   ]
-  const page = new TopicDiscoveryPage({ memoDb: makeMemoDb({ topics }) })
-
-  await page.load()
+  const page = await loadPage(topics)
 
   assert.deepEqual(page.getTopic('bitcoin'), { room: 'bitcoin', postCount: 2 })
 })
 
 test('getTopic returns null when the topic is not loaded', async () => {
-  const page = new TopicDiscoveryPage({ memoDb: makeMemoDb({ topics: [] }) })
-
-  await page.load()
+  const page = await loadPage([])
 
   assert.equal(page.getTopic('bitcoin'), null)
 })
 
 test('getLastSeenLabel formats the topic last-seen time', async () => {
-  const page = new TopicDiscoveryPage({
-    memoDb: makeMemoDb({ topics: [{ room: 'bitcoin', postCount: 1, lastSeen: 1799998200000 }] })
-  })
-
-  await page.load()
+  const page = await loadPage([{ room: 'bitcoin', postCount: 1, lastSeen: 1799998200000 }])
 
   assert.equal(page.getLastSeenLabel('bitcoin', 1800000000000), 'Less than an hour ago')
 })
 
 test('getLastSeenLabel returns "No posts" for a topic with no posts', async () => {
-  const page = new TopicDiscoveryPage({
-    memoDb: makeMemoDb({ topics: [{ room: 'lone', postCount: 0, lastSeen: 0 }] })
-  })
-
-  await page.load()
+  const page = await loadPage([{ room: 'lone', postCount: 0, lastSeen: 0 }])
 
   assert.equal(page.getLastSeenLabel('lone', 1800000000000), 'No posts')
 })
 
 test('getLastSeenLabel returns null for an unknown topic', async () => {
-  const page = new TopicDiscoveryPage({ memoDb: makeMemoDb({ topics: [] }) })
-
-  await page.load()
+  const page = await loadPage([])
 
   assert.equal(page.getLastSeenLabel('missing', 1800000000000), null)
 })

psf-memo-db/test/property/backfill-topic-indexes.property.test.js

@@ -6,8 +6,9 @@
   contents:
 
     - Conservation: every room in the rooms store gets a summary whose
-      postCount equals its number of post entries and whose lastHeight is the
-      newest post height (0 for follow-only rooms).
+      postCount equals its number of post entries, whose lastHeight is the
+      newest post height and lastSeen the newest post time (0 for follow-only
+      rooms), and whose followerCount equals its number of active follows.
     - Recency shape: topicRecency holds exactly one record per summarized room,
       keyed at that room's lastHeight, with the matching value.
     - Idempotence: running the backfill twice produces identical indexes, and
@@ -20,40 +21,13 @@ import test from 'node:test'
 
 import { seededRandom, forAll, intGen } from './harness.js'
 import { backfillTopicIndexes, topicRecencyKey } from '../../src/lib/backfill-topic-indexes.js'
+import { FakeDb } from '../support/level-double.js'
 
 const rng = seededRandom(20260917)
 
 const ROOMS = ['room-0', 'room-1', 'room-2', 'room-3']
 const FOLLOW_ADDRS = ['addr-0', 'addr-1', 'addr-2']
 
-// In-memory LevelDB-shaped store supporting the iterator/get/put/del surface
-// the backfill uses.
-function makeDb (records = []) {
-  const store = new Map(records)
-  return {
-    store,
-    async get (key) {
-      if (!store.has(key)) {
-        const err = new Error('not found')
-        err.notFound = true
-        throw err
-      }
-      return store.get(key)
-    },
-    async put (key, value) {
-      store.set(key, value)
-    },
-    async del (key) {
-      store.delete(key)
-    },
-    async * iterator () {
-      for (const key of Array.from(store.keys()).sort()) {
-        yield [key, store.get(key)]
-      }
-    }
-  }
-}
-
 // Random rooms-store contents: each room gets a random number of posts and
 // follow records, including unfollows and follows with no posts.
 function roomsGen () {
@@ -65,7 +39,7 @@ function roomsGen () {
       for (let i = 0; i < postCount; i++) {
         entries.push([
           `${room}:post-${seq}`,
-          { room, txid: `post-${seq}`, type: 'post', blockHeight: intGen(rng, 0, 9000000)() }
+          { room, txid: `post-${seq}`, type: 'post', blockHeight: intGen(rng, 0, 9000000)(), seen: intGen(rng, 0, 5000000)() }
         ])
         seq++
       }
@@ -88,12 +62,18 @@ function expectedSummaries (entries) {
   const summaries = new Map()
   for (const [, value] of entries) {
     const room = value.room
-    if (!summaries.has(room)) summaries.set(room, { room, postCount: 0, lastHeight: 0 })
-    if (value.type === 'post') {
+    if (!summaries.has(room)) {
+      summaries.set(room, { room, postCount: 0, lastHeight: 0, lastSeen: 0, followerCount: 0 })
+    }
     const summary = summaries.get(room)
+    if (value.type === 'post') {
       summary.postCount++
       const height = value.blockHeight ?? 0
       if (height > summary.lastHeight) summary.lastHeight = height
+      const seen = value.seen ?? 0
+      if (seen > summary.lastSeen) summary.lastSeen = seen
+    } else if (value.type === 'follow' && value.unfollow !== true) {
+      summary.followerCount++
     }
   }
   return summaries
@@ -107,9 +87,9 @@ test('backfill conserves every room summary and builds the recency index', async
   await forAll(
     roomsGen(),
     async (entries) => {
-      const roomsDb = makeDb(entries)
-      const topicSummariesDb = makeDb()
-      const topicRecencyDb = makeDb()
+      const roomsDb = new FakeDb(entries)
+      const topicSummariesDb = new FakeDb()
+      const topicRecencyDb = new FakeDb()
 
       const result = await backfillTopicIndexes({ roomsDb, topicSummariesDb, topicRecencyDb })
 
@@ -122,6 +102,8 @@ test('backfill conserves every room summary and builds the recency index', async
         if (!stored) return false
         if (stored.postCount !== summary.postCount) return false
         if (stored.lastHeight !== summary.lastHeight) return false
+        if (stored.lastSeen !== summary.lastSeen) return false
+        if (stored.followerCount !== summary.followerCount) return false
 
         const key = topicRecencyKey(summary.lastHeight, room)
         const recency = topicRecencyDb.store.get(key)
@@ -150,11 +132,11 @@ test('backfill drops stale recency and summary records from earlier runs', async
   await forAll(
     roomsGen(),
     async (entries) => {
-      const roomsDb = makeDb(entries)
-      const topicSummariesDb = makeDb([
+      const roomsDb = new FakeDb(entries)
+      const topicSummariesDb = new FakeDb([
         ['stale-room', { room: 'stale-room', postCount: 9, lastHeight: 999999 }]
       ])
-      const topicRecencyDb = makeDb([
+      const topicRecencyDb = new FakeDb([
         [topicRecencyKey(999999, 'stale-room'), { room: 'stale-room', blockHeight: 999999 }],
         [topicRecencyKey(123456, 'another-stale'), { room: 'another-stale', blockHeight: 123456 }]
       ])

psf-memo-db/test/property/topic-query.property.test.js

@@ -7,7 +7,8 @@
 
     - listTopics conservation: the sum of postCounts equals the number of
       post entries in the rooms store, each room's count matches its own post
-      entries, and the topics are returned sorted by most recent post.
+      entries, each room's lastSeen and followerCount match its post times and
+      active follows, and the topics are returned sorted by most recent post.
     - getTopicPostTxids ordering + pagination: posts are returned newest-first
       by block height, the total matches the room's post entries, and the
       offset/limit slice is exact.
@@ -72,12 +73,18 @@ function indexDbsFromEntries (entries) {
   const summaries = new Map()
   for (const e of entries) {
     const room = e.value.room
-    if (!summaries.has(room)) summaries.set(room, { room, postCount: 0, lastHeight: 0 })
-    if (e.value.type === 'post') {
+    if (!summaries.has(room)) {
+      summaries.set(room, { room, postCount: 0, lastHeight: 0, lastSeen: 0, followerCount: 0 })
+    }
     const summary = summaries.get(room)
+    if (e.value.type === 'post') {
       summary.postCount++
       const height = e.value.blockHeight ?? 0
       if (height > summary.lastHeight) summary.lastHeight = height
+      const seen = e.value.seen ?? 0
+      if (seen > summary.lastSeen) summary.lastSeen = seen
+    } else if (e.value.type === 'follow' && e.value.unfollow !== true) {
+      summary.followerCount++
     }
   }
 
@@ -132,6 +139,7 @@ function fixtureGen () {
             txid: txidGen(rng),
             addr: ADDRESSES[intGen(rng, 0, ADDRESSES.length - 1)()],
             blockHeight: intGen(rng, 0, 9000000)(),
+            seen: intGen(rng, 0, 5000000)(),
             room
           }
         })
@@ -141,7 +149,7 @@ function fixtureGen () {
       for (let j = 0; j < followCount; j++) {
         entries.push({
           key: `${room}:${txidGen(rng)}`,
-          value: { type: 'follow', room }
+          value: { type: 'follow', room, unfollow: rng() < 0.4 }
         })
       }
     }
@@ -169,10 +177,18 @@ test('listTopics conserves post counts and returns rooms sorted by most recent p
       const postEntries = entries.filter((e) => e.value.type === 'post')
       const expectedTopics = [...new Set(entries.map((e) => e.value.room))]
         .map((room) => {
-          const heights = entries
-            .filter((e) => e.value.room === room && e.value.type === 'post')
-            .map((e) => e.value.blockHeight ?? 0)
-          return { room, lastHeight: heights.length ? Math.max(...heights) : 0 }
+          const roomPosts = entries.filter((e) => e.value.room === room && e.value.type === 'post')
+          const heights = roomPosts.map((e) => e.value.blockHeight ?? 0)
+          const seens = roomPosts.map((e) => e.value.seen ?? 0)
+          const followerCount = entries.filter(
+            (e) => e.value.room === room && e.value.type === 'follow' && e.value.unfollow !== true
+          ).length
+          return {
+            room,
+            lastHeight: heights.length ? Math.max(...heights) : 0,
+            lastSeen: seens.length ? Math.max(...seens) : 0,
+            followerCount
+          }
         })
         .sort((a, b) => {
           if (b.lastHeight !== a.lastHeight) return b.lastHeight - a.lastHeight
@@ -186,8 +202,12 @@ test('listTopics conserves post counts and returns rooms sorted by most recent p
       if (pagination.hasMore !== (offset + topics.length < pagination.total)) return false
 
       for (const topic of topics) {
+        const expectedTopic = expectedTopics.find((t) => t.room === topic.room)
+        if (!expectedTopic) return false
         const roomPosts = postEntries.filter((e) => e.value.room === topic.room).length
         if (topic.postCount !== roomPosts) return false
+        if (topic.lastSeen !== expectedTopic.lastSeen) return false
+        if (topic.followerCount !== expectedTopic.followerCount) return false
       }
       return true
     },

psf-memo-db/test/support/level-double.js

@@ -1,15 +1,21 @@
 /*
-  In-memory LevelDB double shared by the txid repair unit and property tests.
+  In-memory LevelDB double shared by the txid repair and topic index unit and
+  property tests.
 
-  FakeDb implements just the get/put/del/iterator surface the repair library
-  uses, plus keys() for assertions. makeLevel() wires the same store names the
-  real psf-memo-db exposes so the repair library can be driven without opening
-  any real LevelDB files.
+  FakeDb implements the get/put/del/iterator surface the libraries use, honors
+  the `gte`/`lte`/`limit` iterator options the topic read path relies on, and
+  exposes the backing Map as `store` for assertions. makeLevel() wires the same
+  store names the real psf-memo-db exposes so the repair library can be driven
+  without opening any real LevelDB files.
 */
 
 export class FakeDb {
-  constructor () {
-    this.map = new Map()
+  constructor (records = []) {
+    this.map = new Map(records)
+  }
+
+  get store () {
+    return this.map
   }
 
   async get (key) {
@@ -29,9 +35,13 @@ export class FakeDb {
     this.map.delete(key)
   }
 
-  async * iterator () {
-    for (const [key, value] of this.map) {
-      yield [key, value]
+  async * iterator (opts = {}) {
+    let keys = [...this.map.keys()].sort()
+    if (opts.gte !== undefined) keys = keys.filter((key) => key >= opts.gte)
+    if (opts.lte !== undefined) keys = keys.filter((key) => key <= opts.lte)
+    const limit = opts.limit === undefined ? keys.length : opts.limit
+    for (const key of keys.slice(0, limit)) {
+      yield [key, this.map.get(key)]
     }
   }
 

psf-memo-db/test/unit/adapters/topic-query.unit.js

@@ -2,65 +2,16 @@ import { assert } from 'chai'
 import sinon from 'sinon'
 import TopicQuery from '../../../src/adapters/topic-query.js'
 import { topicRecencyKey } from '../../../src/lib/backfill-topic-indexes.js'
+import { FakeDb } from '../../support/level-double.js'
 
 function makeRoomsDb (records = {}) {
-  const store = new Map(Object.entries(records))
-  return {
-    async get (key) {
-      if (!store.has(key)) {
-        const err = new Error('not found')
-        err.notFound = true
-        throw err
-      }
-      return store.get(key)
-    },
-    iterator (opts = {}) {
-      const entries = Array.from(store.entries()).sort((a, b) => a[0].localeCompare(b[0]))
-      const { gte, lte } = opts
-      const filtered = entries.filter(([key]) => {
-        if (gte && key < gte) return false
-        if (lte && key > lte) return false
-        return true
-      })
-      let i = 0
-      return {
-        [Symbol.asyncIterator] () {
-          return this
-        },
-        async next () {
-          if (i >= filtered.length) return { value: undefined, done: true }
-          const entry = filtered[i++]
-          return { value: entry, done: false }
-        },
-        async close () {}
-      }
-    }
-  }
+  return new FakeDb(Object.entries(records))
 }
 
 // In-memory index store whose iterator honors the LevelDB `limit` option, so
 // the read path's bounded recency reads can be asserted.
 function makeIteratorDb (records = []) {
-  const store = new Map(records)
-  return {
-    async get (key) {
-      if (!store.has(key)) {
-        const err = new Error('not found')
-        err.notFound = true
-        throw err
-      }
-      return store.get(key)
-    },
-    async * iterator (opts = {}) {
-      let keys = Array.from(store.keys()).sort()
-      if (opts.gte !== undefined) keys = keys.filter((k) => k >= opts.gte)
-      if (opts.lte !== undefined) keys = keys.filter((k) => k <= opts.lte)
-      const limit = opts.limit === undefined ? keys.length : opts.limit
-      for (const key of keys.slice(0, limit)) {
-        yield [key, store.get(key)]
-      }
-    }
-  }
+  return new FakeDb(records)
 }
 
 describe('#TopicQuery', () => {
@@ -128,15 +79,20 @@ describe('#TopicQuery', () => {
     }
   })
 
-  describe('#roomFromKey', () => {
+  for (const { method, presentKey, fallbackKey } of [
+    { method: 'roomFromKey', presentKey: 'ignored:post-1', fallbackKey: 'cash:post-1' },
+    { method: 'summaryRoom', presentKey: 'ignored', fallbackKey: 'cash' }
+  ]) {
+    describe(`#${method}`, () => {
       it('should return the room from the value when present', () => {
-      assert.equal(uut.roomFromKey('ignored:post-1', { room: 'bitcoin' }), 'bitcoin')
+        assert.equal(uut[method](presentKey, { room: 'bitcoin' }), 'bitcoin')
       })
 
-    it('should fall back to the first segment of the key', () => {
-      assert.equal(uut.roomFromKey('cash:post-1', {}), 'cash')
+      it('should fall back to the key when the value omits the room', () => {
+        assert.equal(uut[method](fallbackKey, {}), 'cash')
       })
     })
+  }
 
   describe('#txidFromKey', () => {
     it('should return the last segment of the key', () => {
@@ -144,16 +100,6 @@ describe('#TopicQuery', () => {
     })
   })
 
-  describe('#summaryRoom', () => {
-    it('should return the room from the value when present', () => {
-      assert.equal(uut.summaryRoom('ignored', { room: 'bitcoin' }), 'bitcoin')
-    })
-
-    it('should fall back to the key when the value omits the room', () => {
-      assert.equal(uut.summaryRoom('cash', {}), 'cash')
-    })
-  })
-
   describe('#recencyRoom', () => {
     it('should return the room from the value when present', () => {
       assert.equal(uut.recencyRoom('ignored', { room: 'bitcoin' }), 'bitcoin')
@@ -222,7 +168,11 @@ describe('#TopicQuery', () => {
       ])
     })
 
-    it('should paginate using recency order and report total and hasMore', async () => {
+    for (const { name, limit, offset, expectedRooms, hasMore } of [
+      { name: 'should paginate using recency order and report total and hasMore', limit: 2, offset: 2, expectedRooms: ['dance', 'anime'], hasMore: true },
+      { name: 'should report hasMore false on the last page', limit: 2, offset: 4, expectedRooms: ['lone', 'quiet'], hasMore: false }
+    ]) {
+      it(name, async () => {
         uut = new TopicQuery({
           roomsDb,
           postsDb,
@@ -230,27 +180,13 @@ describe('#TopicQuery', () => {
           topicRecencyDb: makeIteratorDb(recency)
         })
 
-      const result = await uut.listTopics({ limit: 2, offset: 2 })
+        const result = await uut.listTopics({ limit, offset })
 
-      assert.deepEqual(result.topics.map((t) => t.room), ['dance', 'anime'])
+        assert.deepEqual(result.topics.map((t) => t.room), expectedRooms)
         assert.equal(result.pagination.total, 6)
-      assert.equal(result.pagination.hasMore, true)
-    })
-
-    it('should report hasMore false on the last page', async () => {
-      uut = new TopicQuery({
-        roomsDb,
-        postsDb,
-        topicSummariesDb: makeIteratorDb(summaries),
-        topicRecencyDb: makeIteratorDb(recency)
-      })
-
-      const result = await uut.listTopics({ limit: 2, offset: 4 })
-
-      assert.deepEqual(result.topics.map((t) => t.room), ['lone', 'quiet'])
-      assert.equal(result.pagination.total, 6)
-      assert.equal(result.pagination.hasMore, false)
+        assert.equal(result.pagination.hasMore, hasMore)
       })
+    }
 
     it('should read the recency index without iterating the rooms store', async () => {
       uut = new TopicQuery({
@@ -283,7 +219,11 @@ describe('#TopicQuery', () => {
       assert.equal(result.total, 2)
     })
 
-    it('should paginate topic posts', async () => {
+    for (const { name, limit, offset, txids } of [
+      { name: 'should paginate topic posts', limit: 1, offset: 0, txids: ['post-300'] },
+      { name: 'should apply offset', limit: 100, offset: 1, txids: ['post-200'] }
+    ]) {
+      it(name, async () => {
         async function * mockRooms () {
           yield ['bitcoin:post-300', { room: 'bitcoin', txid: 'post-300', type: 'post', blockHeight: 300 }]
           yield ['bitcoin:post-200', { room: 'bitcoin', txid: 'post-200', type: 'post', blockHeight: 200 }]
@@ -292,26 +232,12 @@ describe('#TopicQuery', () => {
           .withArgs(sinon.match({ gte: 'bitcoin:', lte: 'bitcoin:\uffff' }))
           .returns(mockRooms())
 
-      const result = await uut.getTopicPostTxids('bitcoin', { limit: 1, offset: 0 })
+        const result = await uut.getTopicPostTxids('bitcoin', { limit, offset })
 
-      assert.deepEqual(result.txids, ['post-300'])
+        assert.deepEqual(result.txids, txids)
         assert.equal(result.total, 2)
       })
-
-    it('should apply offset', async () => {
-      async function * mockRooms () {
-        yield ['bitcoin:post-300', { room: 'bitcoin', txid: 'post-300', type: 'post', blockHeight: 300 }]
-        yield ['bitcoin:post-200', { room: 'bitcoin', txid: 'post-200', type: 'post', blockHeight: 200 }]
     }
-      roomsDb.iterator
-        .withArgs(sinon.match({ gte: 'bitcoin:', lte: 'bitcoin:\uffff' }))
-        .returns(mockRooms())
-
-      const result = await uut.getTopicPostTxids('bitcoin', { limit: 100, offset: 1 })
-
-      assert.deepEqual(result.txids, ['post-200'])
-      assert.equal(result.total, 2)
-    })
 
     it('should return empty result for a topic with no posts', async () => {
       async function * empty () {}
@@ -392,19 +318,17 @@ describe('#TopicQuery', () => {
       assert.equal(result, false)
     })
 
-    it('should return true for an active follow record', async () => {
-      roomsDb.get.withArgs('bitcoin:addr-a').resolves({ room: 'bitcoin', addr: 'addr-a', type: 'follow', unfollow: false })
+    for (const { addr, unfollow, expected } of [
+      { addr: 'addr-a', unfollow: false, expected: true },
+      { addr: 'addr-c', unfollow: true, expected: false }
+    ]) {
+      it(`should return ${expected} for a follow record with unfollow ${unfollow}`, async () => {
+        roomsDb.get.withArgs(`bitcoin:${addr}`).resolves({ room: 'bitcoin', addr, type: 'follow', unfollow })
 
-      const result = await uut.isFollowingRoom('addr-a', 'bitcoin')
-      assert.equal(result, true)
-    })
-
-    it('should return false for an unfollow record', async () => {
-      roomsDb.get.withArgs('bitcoin:addr-c').resolves({ room: 'bitcoin', addr: 'addr-c', type: 'follow', unfollow: true })
-
-      const result = await uut.isFollowingRoom('addr-c', 'bitcoin')
-      assert.equal(result, false)
+        const result = await uut.isFollowingRoom(addr, 'bitcoin')
+        assert.equal(result, expected)
       })
+    }
 
     it('should return false for a non-follow record', async () => {
       roomsDb.get.withArgs('bitcoin:addr-a').resolves({ room: 'bitcoin', txid: 'post-1', type: 'post' })

psf-memo-db/test/unit/lib/backfill-topic-indexes.unit.js

@@ -1,43 +1,18 @@
 import { assert } from 'chai'
 import { backfillTopicIndexes, topicRecencyKey } from '../../../src/lib/backfill-topic-indexes.js'
-
-function makeDb (records = []) {
-  const store = new Map(records)
-  return {
-    store,
-    async get (key) {
-      if (!store.has(key)) {
-        const err = new Error('not found')
-        err.notFound = true
-        throw err
-      }
-      return store.get(key)
-    },
-    async put (key, value) {
-      store.set(key, value)
-    },
-    async del (key) {
-      store.delete(key)
-    },
-    async * iterator () {
-      for (const key of Array.from(store.keys()).sort()) {
-        yield [key, store.get(key)]
-      }
-    }
-  }
-}
+import { FakeDb } from '../../support/level-double.js'
 
 describe('#backfillTopicIndexes', () => {
   it('should summarize rooms with posts and follow-only rooms', async () => {
-    const roomsDb = makeDb([
+    const roomsDb = new FakeDb([
       ['bitcoin:post-100', { room: 'bitcoin', txid: 'post-100', type: 'post', blockHeight: 600100, seen: 1700000000000 }],
       ['bitcoin:post-200', { room: 'bitcoin', txid: 'post-200', type: 'post', blockHeight: 600200, seen: 1700000999000 }],
       ['bitcoin:addr-f', { room: 'bitcoin', addr: 'addr-f', type: 'follow', unfollow: false }],
       ['cash:post-250', { room: 'cash', txid: 'post-250', type: 'post', blockHeight: 600250, seen: 1700002000000 }],
       ['lone:addr-f', { room: 'lone', addr: 'addr-f', type: 'follow', unfollow: false }]
     ])
-    const topicSummariesDb = makeDb()
-    const topicRecencyDb = makeDb()
+    const topicSummariesDb = new FakeDb()
+    const topicRecencyDb = new FakeDb()
 
     const result = await backfillTopicIndexes({ roomsDb, topicSummariesDb, topicRecencyDb })
 
@@ -71,13 +46,13 @@ describe('#backfillTopicIndexes', () => {
   })
 
   it('should count only active follows and ignore unfollowed addresses', async () => {
-    const roomsDb = makeDb([
+    const roomsDb = new FakeDb([
       ['bitcoin:addr-a', { room: 'bitcoin', addr: 'addr-a', type: 'follow', unfollow: false }],
       ['bitcoin:addr-b', { room: 'bitcoin', addr: 'addr-b', type: 'follow', unfollow: true }],
       ['bitcoin:addr-c', { room: 'bitcoin', addr: 'addr-c', type: 'follow', unfollow: false }]
     ])
-    const topicSummariesDb = makeDb()
-    const topicRecencyDb = makeDb()
+    const topicSummariesDb = new FakeDb()
+    const topicRecencyDb = new FakeDb()
 
     await backfillTopicIndexes({ roomsDb, topicSummariesDb, topicRecencyDb })
 
@@ -85,12 +60,12 @@ describe('#backfillTopicIndexes', () => {
   })
 
   it('should keep the newest lastSeen when post heights and seen times disagree', async () => {
-    const roomsDb = makeDb([
+    const roomsDb = new FakeDb([
       ['bitcoin:post-100', { room: 'bitcoin', txid: 'post-100', type: 'post', blockHeight: 600100, seen: 1700009999000 }],
       ['bitcoin:post-200', { room: 'bitcoin', txid: 'post-200', type: 'post', blockHeight: 600200, seen: 1700000000000 }]
     ])
-    const topicSummariesDb = makeDb()
-    const topicRecencyDb = makeDb()
+    const topicSummariesDb = new FakeDb()
+    const topicRecencyDb = new FakeDb()
 
     await backfillTopicIndexes({ roomsDb, topicSummariesDb, topicRecencyDb })
 
@@ -100,12 +75,12 @@ describe('#backfillTopicIndexes', () => {
   })
 
   it('should be idempotent across repeated runs', async () => {
-    const roomsDb = makeDb([
+    const roomsDb = new FakeDb([
       ['bitcoin:post-200', { room: 'bitcoin', txid: 'post-200', type: 'post', blockHeight: 600200, seen: 1700003000000 }],
       ['lone:addr-f', { room: 'lone', addr: 'addr-f', type: 'follow', unfollow: false }]
     ])
-    const topicSummariesDb = makeDb()
-    const topicRecencyDb = makeDb()
+    const topicSummariesDb = new FakeDb()
+    const topicRecencyDb = new FakeDb()
 
     await backfillTopicIndexes({ roomsDb, topicSummariesDb, topicRecencyDb })
     const firstSummaries = new Map(topicSummariesDb.store)
@@ -118,11 +93,11 @@ describe('#backfillTopicIndexes', () => {
   })
 
   it('should remove stale recency records from a previous run', async () => {
-    const roomsDb = makeDb([
+    const roomsDb = new FakeDb([
       ['bitcoin:post-200', { room: 'bitcoin', txid: 'post-200', type: 'post', blockHeight: 600200, seen: 1700000000000 }]
     ])
-    const topicSummariesDb = makeDb()
-    const topicRecencyDb = makeDb([
+    const topicSummariesDb = new FakeDb()
+    const topicRecencyDb = new FakeDb([
       [topicRecencyKey(600100, 'bitcoin'), { room: 'bitcoin', blockHeight: 600100 }],
       [topicRecencyKey(0, 'stale'), { room: 'stale', blockHeight: 0 }]
     ])
@@ -135,11 +110,11 @@ describe('#backfillTopicIndexes', () => {
   })
 
   it('should fall back to the key room segment when a record omits the room', async () => {
-    const roomsDb = makeDb([
+    const roomsDb = new FakeDb([
       ['cash:post-1', { type: 'post', blockHeight: 500 }]
     ])
-    const topicSummariesDb = makeDb()
-    const topicRecencyDb = makeDb()
+    const topicSummariesDb = new FakeDb()
+    const topicRecencyDb = new FakeDb()
 
     await backfillTopicIndexes({ roomsDb, topicSummariesDb, topicRecencyDb })
 

psf-memo-indexer/src/use-cases/action-types/topic-indexing.js

@@ -77,7 +77,7 @@ export async function recordTopicFollow (adapters, record) {
   if (!existing && !isActive) return null
 
   const summary = existing || await ensureTopicRoom(adapters, room)
-  const delta = (isActive ? 1 : 0) - (wasActive ? 1 : 0)
+  const delta = Number(isActive) - Number(wasActive)
   if (delta === 0) return summary
 
   const updated = {

psf-memo-indexer/test/property/topic-indexing.property.test.js

@@ -7,8 +7,10 @@
   follows, and unfollows:
 
     - Conservation: each room's summary postCount equals the number of distinct
-      topic-message txids seen for that room, and lastHeight equals the newest
-      post height (0 when the room has no posts).
+      topic-message txids seen for that room, lastHeight equals the newest
+      post height and lastSeen the newest post time (both 0 when the room has
+      no posts), and followerCount equals the number of addresses whose final
+      follow state for the room is active.
     - Recency shape: topicRecency holds exactly one record per summarized room,
       keyed at that room's lastHeight, with the matching value.
     - Idempotence: replaying the whole action sequence leaves every index
@@ -24,48 +26,22 @@ import { handleTopicMessage } from '../../src/use-cases/action-types/topic-messa
 import { handleTopicFollow } from '../../src/use-cases/action-types/topic-follow.js'
 import { topicRecencyKey } from '../../src/use-cases/action-types/helpers.js'
 import { PREFIX_TOPIC_FOLLOW, PREFIX_TOPIC_UNFOLLOW } from '../../src/lib/memo-codes.js'
+import { makeMemoryDb } from '../support/memory-db.js'
 
 const rng = seededRandom(20260917)
 
 const ROOMS = ['room-0', 'room-1', 'room-2', 'room-3']
 const FOLLOW_ADDRS = ['bitcoincash:qaddr-0', 'bitcoincash:qaddr-1', 'bitcoincash:qaddr-2']
 
-function makeDb () {
-  const store = new Map()
-  return {
-    store,
-    async get (key) {
-      if (!store.has(key)) {
-        const err = new Error('not found')
-        err.notFound = true
-        throw err
-      }
-      return store.get(key)
-    },
-    async create (key, value) {
-      if (!store.has(key)) store.set(key, value)
-      return { success: true }
-    },
-    async update (key, value) {
-      store.set(key, value)
-      return { success: true }
-    },
-    async delete (key) {
-      store.delete(key)
-      return { success: true }
-    }
-  }
-}
-
 function makeAdapters () {
   return {
-    postDb: makeDb(),
-    postHeightDb: makeDb(),
-    addrPostHeightDb: makeDb(),
-    roomDb: makeDb(),
-    topicSummaryDb: makeDb(),
-    topicRecencyDb: makeDb(),
-    processErrorDb: makeDb()
+    postDb: makeMemoryDb(),
+    postHeightDb: makeMemoryDb(),
+    addrPostHeightDb: makeMemoryDb(),
+    roomDb: makeMemoryDb(),
+    topicSummaryDb: makeMemoryDb(),
+    topicRecencyDb: makeMemoryDb(),
+    processErrorDb: makeMemoryDb()
   }
 }
 
@@ -76,7 +52,7 @@ async function processEvent (adapters, event) {
       adapters,
       txid: event.txid,
       signerAddr: 'bitcoincash:qauthor',
-      seen: 1,
+      seen: event.seen,
       blockHeight: event.height,
       decoded: {
         action: 'topic-message',
@@ -117,6 +93,7 @@ function eventSequenceGen () {
           txid: `txid-${i}`,
           room,
           height: intGen(rng, 0, 9000000)(),
+          seen: intGen(rng, 0, 5000000)(),
           text: `text-${i}`
         })
       } else {
@@ -135,11 +112,15 @@ function eventSequenceGen () {
 }
 
 // Expected summaries derived straight from the event list, independent of the
-// implementation under test.
+// implementation under test. Follower counts use each address's final
+// follow/unfollow state per room.
 function expectedSummaries (events) {
   const summaries = new Map()
+  const followState = new Map()
   const ensure = (room) => {
-    if (!summaries.has(room)) summaries.set(room, { room, postCount: 0, lastHeight: 0 })
+    if (!summaries.has(room)) {
+      summaries.set(room, { room, postCount: 0, lastHeight: 0, lastSeen: 0, followerCount: 0 })
+    }
     return summaries.get(room)
   }
 
@@ -148,12 +129,18 @@ function expectedSummaries (events) {
       const summary = ensure(event.room)
       summary.postCount++
       if (event.height > summary.lastHeight) summary.lastHeight = event.height
-    } else if (!event.unfollow) {
+      if (event.seen > summary.lastSeen) summary.lastSeen = event.seen
+    } else {
+      followState.set(`${event.room}:${event.addr}`, { room: event.room, unfollow: event.unfollow })
       // Only an active follow creates a zero-post room; unfollows do not.
-      ensure(event.room)
+      if (!event.unfollow) ensure(event.room)
     }
   }
 
+  for (const { room, unfollow } of followState.values()) {
+    if (!unfollow && summaries.has(room)) summaries.get(room).followerCount++
+  }
+
   return summaries
 }
 
@@ -175,13 +162,15 @@ test('topic indexes conserve counts and heights over arbitrary action sequences'
 
       const expected = expectedSummaries(events)
 
-      // Conservation: one summary per room with the exact count and height.
+      // Conservation: one summary per room with the exact counts and times.
       if (adapters.topicSummaryDb.store.size !== expected.size) return false
       for (const [room, summary] of expected) {
         const stored = adapters.topicSummaryDb.store.get(room)
         if (!stored) return false
         if (stored.postCount !== summary.postCount) return false
         if (stored.lastHeight !== summary.lastHeight) return false
+        if (stored.lastSeen !== summary.lastSeen) return false
+        if (stored.followerCount !== summary.followerCount) return false
       }
 
       // Recency shape: exactly one record per room, at its lastHeight.

psf-memo-indexer/test/support/memory-db.js

@@ -0,0 +1,32 @@
+/*
+  In-memory LevelDB double shared by the Memo action-type unit and property
+  tests. It supports the get/create/update/delete surface the action handlers
+  use and exposes the backing Map as `store` for assertions.
+*/
+
+export function makeMemoryDb () {
+  const store = new Map()
+  return {
+    store,
+    async get (key) {
+      if (!store.has(key)) {
+        const err = new Error('not found')
+        err.notFound = true
+        throw err
+      }
+      return store.get(key)
+    },
+    async create (key, value) {
+      if (!store.has(key)) store.set(key, value)
+      return { success: true }
+    },
+    async update (key, value) {
+      store.set(key, value)
+      return { success: true }
+    },
+    async delete (key) {
+      store.delete(key)
+      return { success: true }
+    }
+  }
+}

psf-memo-indexer/test/unit/use-cases/action-types/topic-follow.unit.js

@@ -2,40 +2,14 @@ import { assert } from 'chai'
 import { handleTopicFollow } from '../../../../src/use-cases/action-types/topic-follow.js'
 import { PREFIX_TOPIC_FOLLOW, PREFIX_TOPIC_UNFOLLOW } from '../../../../src/lib/memo-codes.js'
 import { topicRecencyKey } from '../../../../src/use-cases/action-types/helpers.js'
-
-function makeDb () {
-  const store = new Map()
-  return {
-    store,
-    async get (key) {
-      if (!store.has(key)) {
-        const err = new Error('not found')
-        err.notFound = true
-        throw err
-      }
-      return store.get(key)
-    },
-    async create (key, value) {
-      store.set(key, value)
-      return { success: true }
-    },
-    async update (key, value) {
-      store.set(key, value)
-      return { success: true }
-    },
-    async delete (key) {
-      store.delete(key)
-      return { success: true }
-    }
-  }
-}
+import { makeMemoryDb } from '../../../support/memory-db.js'
 
 function makeAdapters () {
   return {
-    roomDb: makeDb(),
-    topicSummaryDb: makeDb(),
-    topicRecencyDb: makeDb(),
-    processErrorDb: makeDb()
+    roomDb: makeMemoryDb(),
+    topicSummaryDb: makeMemoryDb(),
+    topicRecencyDb: makeMemoryDb(),
+    processErrorDb: makeMemoryDb()
   }
 }
 
@@ -114,70 +88,63 @@ describe('#handleTopicFollow topic indexes', () => {
     assert.equal(adapters.topicRecencyDb.store.size, 0)
   })
 
-  it('should count two distinct followers', async () => {
-    const adapters = makeAdapters()
+  const followerAddrA = 'bitcoincash:qaddr-a'
+  const followerAddrB = 'bitcoincash:qaddr-b'
+  const followStep = (txid, addr) => ({ txid, room: 'bitcoin', addr, prefix: PREFIX_TOPIC_FOLLOW })
+  const unfollowStep = (txid, addr) => ({ txid, room: 'bitcoin', addr, prefix: PREFIX_TOPIC_UNFOLLOW })
 
-    await processFollow(adapters, { txid: 'follow-3', room: 'bitcoin', addr: 'bitcoincash:qaddr-a' })
-    await processFollow(adapters, { txid: 'follow-4', room: 'bitcoin', addr: 'bitcoincash:qaddr-b' })
-
-    assert.equal(adapters.topicSummaryDb.store.get('bitcoin').followerCount, 2)
-  })
-
-  it('should decrease the follower count on an unfollow', async () => {
-    const adapters = makeAdapters()
-
-    await processFollow(adapters, { txid: 'follow-5', room: 'bitcoin', addr: 'bitcoincash:qaddr-a' })
-    await processFollow(adapters, { txid: 'follow-6', room: 'bitcoin', addr: 'bitcoincash:qaddr-b' })
-    await processFollow(adapters, {
-      txid: 'unfollow-2',
-      room: 'bitcoin',
-      addr: 'bitcoincash:qaddr-a',
-      prefix: PREFIX_TOPIC_UNFOLLOW
-    })
-
-    assert.equal(adapters.topicSummaryDb.store.get('bitcoin').followerCount, 1)
-  })
-
-  it('should not change the follower count when a follow is reprocessed', async () => {
-    const adapters = makeAdapters()
-
-    await processFollow(adapters, { txid: 'follow-7', room: 'bitcoin', addr: 'bitcoincash:qaddr-a' })
-    await processFollow(adapters, { txid: 'follow-7', room: 'bitcoin', addr: 'bitcoincash:qaddr-a' })
-
-    assert.equal(adapters.topicSummaryDb.store.get('bitcoin').followerCount, 1)
-  })
-
-  it('should not double-decrement when an unfollow is reprocessed', async () => {
-    const adapters = makeAdapters()
-
-    await processFollow(adapters, { txid: 'follow-8', room: 'bitcoin', addr: 'bitcoincash:qaddr-a' })
-    await processFollow(adapters, { txid: 'follow-9', room: 'bitcoin', addr: 'bitcoincash:qaddr-b' })
-    const unfollow = {
-      txid: 'unfollow-3',
-      room: 'bitcoin',
-      addr: 'bitcoincash:qaddr-a',
-      prefix: PREFIX_TOPIC_UNFOLLOW
+  const followerCases = [
+    {
+      name: 'should count two distinct followers',
+      steps: [followStep('follow-3', followerAddrA), followStep('follow-4', followerAddrB)],
+      expected: 2
+    },
+    {
+      name: 'should decrease the follower count on an unfollow',
+      steps: [
+        followStep('follow-5', followerAddrA),
+        followStep('follow-6', followerAddrB),
+        unfollowStep('unfollow-2', followerAddrA)
+      ],
+      expected: 1
+    },
+    {
+      name: 'should not change the follower count when a follow is reprocessed',
+      steps: [followStep('follow-7', followerAddrA), followStep('follow-7', followerAddrA)],
+      expected: 1
+    },
+    {
+      name: 'should not double-decrement when an unfollow is reprocessed',
+      steps: [
+        followStep('follow-8', followerAddrA),
+        followStep('follow-9', followerAddrB),
+        unfollowStep('unfollow-3', followerAddrA),
+        unfollowStep('unfollow-3', followerAddrA)
+      ],
+      expected: 1
+    },
+    {
+      name: 'should let a re-follow increase the count after an unfollow',
+      steps: [
+        followStep('follow-10', followerAddrA),
+        unfollowStep('unfollow-4', followerAddrA),
+        followStep('follow-11', followerAddrA)
+      ],
+      expected: 1
     }
-    await processFollow(adapters, unfollow)
-    await processFollow(adapters, unfollow)
+  ]
 
-    assert.equal(adapters.topicSummaryDb.store.get('bitcoin').followerCount, 1)
-  })
-
-  it('should let a re-follow increase the count after an unfollow', async () => {
+  for (const { name, steps, expected } of followerCases) {
+    it(name, async () => {
       const adapters = makeAdapters()
 
-    await processFollow(adapters, { txid: 'follow-10', room: 'bitcoin', addr: 'bitcoincash:qaddr-a' })
-    await processFollow(adapters, {
-      txid: 'unfollow-4',
-      room: 'bitcoin',
-      addr: 'bitcoincash:qaddr-a',
-      prefix: PREFIX_TOPIC_UNFOLLOW
-    })
-    await processFollow(adapters, { txid: 'follow-11', room: 'bitcoin', addr: 'bitcoincash:qaddr-a' })
+      for (const step of steps) {
+        await processFollow(adapters, step)
+      }
 
-    assert.equal(adapters.topicSummaryDb.store.get('bitcoin').followerCount, 1)
+      assert.equal(adapters.topicSummaryDb.store.get('bitcoin').followerCount, expected)
     })
+  }
 
   it('should log a process error and write nothing when the push data count is invalid', async () => {
     const adapters = makeAdapters()

psf-memo-indexer/test/unit/use-cases/action-types/topic-indexing.unit.js

@@ -1,32 +1,13 @@
 import { assert } from 'chai'
-import { recordTopicPost } from '../../../../src/use-cases/action-types/topic-indexing.js'
+import { recordTopicPost, ensureTopicRoom, recordTopicFollow } from '../../../../src/use-cases/action-types/topic-indexing.js'
 import { topicRecencyKey } from '../../../../src/use-cases/action-types/helpers.js'
-
-function makeDb () {
-  const store = new Map()
-  return {
-    store,
-    async get (key) {
-      if (!store.has(key)) {
-        const err = new Error('not found')
-        err.notFound = true
-        throw err
-      }
-      return store.get(key)
-    },
-    async update (key, value) {
-      store.set(key, value)
-    },
-    async delete (key) {
-      store.delete(key)
-    }
-  }
-}
+import { makeMemoryDb } from '../../../support/memory-db.js'
 
 function makeAdapters () {
   return {
-    topicSummaryDb: makeDb(),
-    topicRecencyDb: makeDb()
+    roomDb: makeMemoryDb(),
+    topicSummaryDb: makeMemoryDb(),
+    topicRecencyDb: makeMemoryDb()
   }
 }
 
@@ -132,3 +113,46 @@ describe('#recordTopicPost lastSeen', () => {
     assert.equal(adapters.topicSummaryDb.store.get('bitcoin').followerCount, 4)
   })
 })
+
+describe('#ensureTopicRoom', () => {
+  it('should return an existing summary unchanged', async () => {
+    const adapters = makeAdapters()
+    const existing = {
+      room: 'bitcoin',
+      postCount: 2,
+      lastHeight: 600100,
+      lastSeen: 1700000000000,
+      followerCount: 3
+    }
+    adapters.topicSummaryDb.store.set('bitcoin', existing)
+
+    const result = await ensureTopicRoom(adapters, 'bitcoin')
+
+    assert.deepEqual(result, existing)
+    assert.equal(adapters.topicRecencyDb.store.size, 0)
+  })
+})
+
+describe('#recordTopicFollow legacy summaries', () => {
+  it('should default a missing follower count to zero', async () => {
+    const adapters = makeAdapters()
+    adapters.topicSummaryDb.store.set('bitcoin', {
+      room: 'bitcoin',
+      postCount: 2,
+      lastHeight: 600100,
+      lastSeen: 1700000000000
+    })
+
+    await recordTopicFollow(adapters, {
+      room: 'bitcoin',
+      addr: 'bitcoincash:qaddr-a',
+      unfollow: false,
+      txid: 'follow-1',
+      seen: 1,
+      type: 'follow',
+      blockHeight: 600100
+    })
+
+    assert.equal(adapters.topicSummaryDb.store.get('bitcoin').followerCount, 1)
+  })
+})

psf-memo-indexer/test/unit/use-cases/action-types/topic-message.unit.js

@@ -2,46 +2,17 @@ import { assert } from 'chai'
 import { handleTopicMessage } from '../../../../src/use-cases/action-types/topic-message.js'
 import { topicRecencyKey } from '../../../../src/use-cases/action-types/helpers.js'
 import { MAX_POST_SIZE } from '../../../../src/lib/memo-codes.js'
-
-function makeDb () {
-  const store = new Map()
-  return {
-    store,
-    async get (key) {
-      if (!store.has(key)) {
-        const err = new Error('not found')
-        err.notFound = true
-        throw err
-      }
-      return store.get(key)
-    },
-    async create (key, value) {
-      store.set(key, value)
-      return { success: true }
-    },
-    async update (key, value) {
-      store.set(key, value)
-      return { success: true }
-    },
-    async delete (key) {
-      store.delete(key)
-      return { success: true }
-    },
-    entries () {
-      return Array.from(store.entries())
-    }
-  }
-}
+import { makeMemoryDb } from '../../../support/memory-db.js'
 
 function makeAdapters () {
   return {
-    postDb: makeDb(),
-    postHeightDb: makeDb(),
-    addrPostHeightDb: makeDb(),
-    roomDb: makeDb(),
-    topicSummaryDb: makeDb(),
-    topicRecencyDb: makeDb(),
-    processErrorDb: makeDb()
+    postDb: makeMemoryDb(),
+    postHeightDb: makeMemoryDb(),
+    addrPostHeightDb: makeMemoryDb(),
+    roomDb: makeMemoryDb(),
+    topicSummaryDb: makeMemoryDb(),
+    topicRecencyDb: makeMemoryDb(),
+    processErrorDb: makeMemoryDb()
   }
 }
 
@@ -61,6 +32,23 @@ async function processTopicMessage (adapters, { txid, room, addr, height, text,
   })
 }
 
+// Process a batch of messages for the bitcoin room.
+async function processMessages (adapters, messages) {
+  for (const message of messages) {
+    await processTopicMessage(adapters, { room: 'bitcoin', addr: 'bitcoincash:qaddr-a', ...message })
+  }
+}
+
+// Assert the room summary and its matching single recency record.
+function assertAccumulatedSummary (adapters, expected) {
+  assert.deepEqual(adapters.topicSummaryDb.store.get('bitcoin'), { room: 'bitcoin', ...expected })
+  assert.deepEqual(adapters.topicRecencyDb.store.get(topicRecencyKey(expected.lastHeight, 'bitcoin')), {
+    room: 'bitcoin',
+    blockHeight: expected.lastHeight
+  })
+  assert.equal(adapters.topicRecencyDb.store.size, 1)
+}
+
 describe('#handleTopicMessage topic indexes', () => {
   it('should record a room summary and a recency record', async () => {
     const adapters = makeAdapters()
@@ -101,45 +89,32 @@ describe('#handleTopicMessage topic indexes', () => {
     assert.equal(adapters.topicSummaryDb.store.get('bitcoin').lastSeen, 1700000000000)
   })
 
-  it('should accumulate postCount and keep the newest height', async () => {
+  const accumulationCases = [
+    {
+      name: 'should accumulate postCount and keep the newest height',
+      messages: [
+        { txid: 'topic-a1', height: 600100, text: 'hello' },
+        { txid: 'topic-a2', height: 600200, text: 'again' }
+      ]
+    },
+    {
+      name: 'should keep the newest height when a later message has an earlier height',
+      messages: [
+        { txid: 'topic-a3', height: 600200, text: 'later' },
+        { txid: 'topic-a4', height: 600100, text: 'earlier' }
+      ]
+    }
+  ]
+
+  for (const { name, messages } of accumulationCases) {
+    it(name, async () => {
       const adapters = makeAdapters()
 
-    await processTopicMessage(adapters, { txid: 'topic-a1', room: 'bitcoin', addr: 'bitcoincash:qaddr-a', height: 600100, text: 'hello' })
-    await processTopicMessage(adapters, { txid: 'topic-a2', room: 'bitcoin', addr: 'bitcoincash:qaddr-a', height: 600200, text: 'again' })
+      await processMessages(adapters, messages)
 
-    assert.deepEqual(adapters.topicSummaryDb.store.get('bitcoin'), {
-      room: 'bitcoin',
-      postCount: 2,
-      lastHeight: 600200,
-      lastSeen: 1,
-      followerCount: 0
-    })
-    assert.deepEqual(adapters.topicRecencyDb.store.get(topicRecencyKey(600200, 'bitcoin')), {
-      room: 'bitcoin',
-      blockHeight: 600200
-    })
-    assert.equal(adapters.topicRecencyDb.store.size, 1)
-  })
-
-  it('should keep the newest height when a later message has an earlier height', async () => {
-    const adapters = makeAdapters()
-
-    await processTopicMessage(adapters, { txid: 'topic-a3', room: 'bitcoin', addr: 'bitcoincash:qaddr-a', height: 600200, text: 'later' })
-    await processTopicMessage(adapters, { txid: 'topic-a4', room: 'bitcoin', addr: 'bitcoincash:qaddr-a', height: 600100, text: 'earlier' })
-
-    assert.deepEqual(adapters.topicSummaryDb.store.get('bitcoin'), {
-      room: 'bitcoin',
-      postCount: 2,
-      lastHeight: 600200,
-      lastSeen: 1,
-      followerCount: 0
-    })
-    assert.deepEqual(adapters.topicRecencyDb.store.get(topicRecencyKey(600200, 'bitcoin')), {
-      room: 'bitcoin',
-      blockHeight: 600200
-    })
-    assert.equal(adapters.topicRecencyDb.store.size, 1)
+      assertAccumulatedSummary(adapters, { postCount: 2, lastHeight: 600200, lastSeen: 1, followerCount: 0 })
     })
+  }
 
   it('should not double-count a reprocessed topic message', async () => {
     const adapters = makeAdapters()