test: add mock db test

test/helper/db-mock.helper.ts

@@ -0,0 +1,45 @@
+import { MongoMemoryServer } from 'mongodb-memory-server'
+import mongoose from 'mongoose'
+
+let mongod: MongoMemoryServer
+
+/**
+ 
+ * Connect to mock memory db.
+ */
+const connect = async () => {
+  mongod = await MongoMemoryServer.create()
+  const uri = mongod.getUri()
+
+  await mongoose.connect(uri, {
+    autoIndex: true,
+    maxPoolSize: 10,
+  })
+}
+
+/**
+ * Close db connection
+ */
+const closeDatabase = async () => {
+  await mongoose.connection.dropDatabase()
+  await mongoose.connection.close()
+  await mongod.stop()
+}
+
+/**
+ * Delete db collections
+ */
+const clearDatabase = async () => {
+  const collections = mongoose.connection.collections
+
+  for (const key in collections) {
+    const collection = collections[key]
+    await collection.deleteMany({})
+  }
+}
+
+export const dbHelper = {
+  connect,
+  close: closeDatabase,
+  clear: clearDatabase,
+}