Is it possible to use Cypress e2e testing with a firebase auth project?

Question

I am exploring Cypress for e2e testing, looks like great software. The problem is Authentication, the Cypress documentation explains why using the UI is very bad here.

So

Answer 1

This is becoming way easier with the upcoming Auth emulator. This has become easier with the Firebase Auth Emulator (firebase-tools >= 8.1.4).

cypress/support/signAs.js:

Cypress.Commands.add('signAs', (uid, opt) => {
  cy.visit('/')

  cy.window().its('firebase').then( fb => {
    cy.wrap( (async _ => {
      // Create a user based on the provided token (only '.uid' is used by Firebase)
      await fb.auth().signInWithCustomToken( JSON.stringify({ uid }) );

      // Set '.displayName', '.photoURL'; for email and password, other functions exist (not implemented)
      await fb.auth().currentUser.updateProfile(opt);
    })() )
  })
})

Use it as:

cy.signAs('joe', { displayName: 'Joe D.', photoURL: 'http://some' });

If you need to set .email or .password, there are similar functions for those, but this was sufficient for my tests. I can now impersonate any user ad-hoc, as part of the test. The approach does not need users to be created in the emulator; you can just claim to be one, with the particular uid. Works well for me.

Note:

Firebase authentication is in IndexedDB (as mentioned in other answers) and Cypress does not clear it, between the tests. There is discussion about this in cypress #1208.