Running Firestore local e.g. for testing

Question

Is there a way to run firestore locally (e.g. for testing purposes)?

What would the approach to write tests against the DB (except of using mocks)

Answer 1

Update 2020:

There's now also a Firebase Emulator Suite.

Update Nov 2018:

Local emulation, at least for the purpose of testing Firestore rules, was demoed at Firebase Summit 2018 using @firestore/testing and documented under Test your Cloud Firestore Security Rules.

It looks like it's along the lines of:

const firebase = require(`@firebase/testing`)
const app = firebase.initializeTestApp({
  projectId: 'my-project',
  auth: { uid: '123', email: 'name@domain.com' }
})

const attempt = app.firestore()
  .collection('colId').doc('docId').get()
firebase.assertFails(attempt)
firebase.assertSucceeds(attempt)

It seems early-on, as it's not been noted in the release-notes, but I'm sure it's coming along.