add user-repository tests

lib/user-repository.js

@@ -0,0 +1,9 @@
+const db = require('./db')
+
+module.exports = {
+  findNotYetReceivedNewsletter: () => {
+    return db.get('users').find({
+      lastEmailSentAt: null
+    })
+  }
+}

lib/user-repository.test.js

@@ -0,0 +1,15 @@
+const test = require('ava')
+const db = require('./db')
+const userRepository = require('./user-repository')
+
+test.beforeEach(async () => {
+  await db.get('users').remove({})
+})
+
+test('find users that did not yet receive the newsletter', async t => {
+  await db.get('users').insert({ name: 'test', email: '[email protected]', lastEmailSentAt: null })
+
+  const users = await userRepository.findNotYetReceivedNewsletter()
+  t.true(Array.isArray(users))
+  t.is(users.length, 1)
+})