Since no one is able to answer the question on stackoverflow and there is no proper doc on this topic. It would be nice to see as a feature request an extension in the angularfire 2 documentation how to properly mock the ref method with getDownloadURL from AngularFireStorageReference.

Link to the stackoverflow question is: here

Version info

Angular: 5.2.4

Firebase: ^4.12.1

AngularFire: ^5.0.0-rc.6