fix(ci): let notification DB tests download mongod when none on PATH

The mongodb-memory-server harness required a system `mongod` and threw on
clean CI runners (no binary on PATH → 3 DB-backed test files failed setup).
Now it uses a system binary when present (offline-friendly local runs) and
falls back to mongodb-memory-server's own download otherwise; CI caches the
downloaded binary across runs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: NateIsern

.github/workflows/ci.yml

@@ -23,6 +23,14 @@ jobs:
       - name: Typecheck (frontend + server)
         run: bun run typecheck
 
+      # The notification DB tests spin up mongodb-memory-server. No system
+      # `mongod` on the runner, so it downloads one — cache it across runs.
+      - name: Cache mongodb-memory-server binary
+        uses: actions/cache@v4
+        with:
+          path: ~/.cache/mongodb-binaries
+          key: mongodb-binaries-${{ runner.os }}
+
       - name: Test
         run: bun run test
 

server/lib/notifications/test-support.ts

@@ -4,29 +4,37 @@ import mongoose from 'mongoose'
 import { MongoMemoryServer } from 'mongodb-memory-server'
 
 // Shared test harness: an in-memory MongoDB the notification DB tests connect
-// mongoose to. It uses the machine's already-installed `mongod` binary
-// (resolved from PATH, overridable via MONGOMS_SYSTEM_BINARY) so tests need no
-// network download. NOT a `*.test.ts` file, so vitest never runs it directly.
+// mongoose to. It prefers an already-installed `mongod` (from PATH, overridable
+// via MONGOMS_SYSTEM_BINARY) so offline/local runs need no download; when none
+// is present (e.g. a clean CI runner) it lets mongodb-memory-server download and
+// cache its own binary. NOT a `*.test.ts` file, so vitest never runs it directly.
 
 let memoryServer: MongoMemoryServer | null = null
 
-/** Locate the `mongod` executable on PATH without invoking a shell. */
-function resolveMongodBinary(): string {
+/**
+ * Locate an already-installed `mongod` (env override, then PATH) without
+ * invoking a shell, or return null when none is found so the caller can fall
+ * back to mongodb-memory-server's own download.
+ */
+function resolveMongodBinary(): string | null {
   const fromEnv = process.env.MONGOMS_SYSTEM_BINARY
   if (fromEnv) return fromEnv
   const dirs = (process.env.PATH ?? '').split(delimiter).filter(Boolean)
   for (const dir of dirs) {
     const candidate = join(dir, 'mongod')
     if (existsSync(candidate)) return candidate
   }
-  throw new Error('mongod not found on PATH; set MONGOMS_SYSTEM_BINARY to its location')
+  return null
 }
 
 /** Boot an in-memory MongoDB and connect mongoose to it. Call in beforeAll. */
 export async function setupMemoryMongo(): Promise<void> {
-  memoryServer = await MongoMemoryServer.create({
-    binary: { systemBinary: resolveMongodBinary() },
-  })
+  const systemBinary = resolveMongodBinary()
+  // Use a system binary when present (no network); otherwise omit `binary` so
+  // mongodb-memory-server resolves, downloads, and caches one itself.
+  memoryServer = await MongoMemoryServer.create(
+    systemBinary ? { binary: { systemBinary } } : undefined,
+  )
   await mongoose.connect(memoryServer.getUri(), { dbName: 'notifications_test' })
 }