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firebase-dbfake is a fake library to assist you in unit testing your JavaScript projects that store data in Firebase.

When you store data in firebase, you have two basic objects that you interact with:

• reference describes the location in your document store you would like to work with
• dataSnapshot a representation of the data at a reference

The book Growing Object Oriented Software, Guided by Tests states that you should never mock interfaces that you don't own. firebase-dbfakes is designed to make it simple for you to obey this principle. When you call once() on a reference, you get back a promise and if all goes well that resolves to a DataSnapshot. The core principle that started firebase-dbfake is that you don't own once() and you should have a shim that calls it. The shim returns you a promise which resolves to a DataSnapshot. Once you have that in place, you can inject a firebase-dbfake.snapshot and unit test to your hearts content.

firebase-dbfake exposes four methods to help you in your unit testing:

• reference returns you an object with the same api as a real Firebase reference, but it doesn't do much of anything. It does enable you to supply your own behavior needed for your tests.
• snapshot returns you an object with the same api as a real Firebase dataSnapshot, but it won't connect to Firebase.
• resolveSnapshot returns a promise that resolves a snapshot. You should use this when you mock your code that would interact with Firebase.
• memoizeSnapshot a short hand for writing a function that returns a promise which resolves a snapshot. Again, used when mocking your data layer.