DocumentDB Emulator

When it comes to developing globally-distributed apps, having the right environment, platforms and tools is of the utmost importance. Over the past years, MongoDB has been one of the main systems of choice for developers who wanted to make sure that their apps are fast, scalable and as widely distributed as possible.

A few words on Microsoft's relatively new NoSQL database service

However, Microsoft wants a piece of the action with their product dubbed DocumentDB that aims to offer a comprehensive alternative for developing fast and cost-effective distributed apps.
Designed to be relevant for mobile, web, and IoT apps alike, DocumentDB is a full-fledged NoSQL database that offers SQL, MongoDB and JavaScript query capabilities and a strong focus on low latency and efficient data replication.

Bespoke testing and development environment for DocumentDB

Having said that, you should be able to make the switch from MongoDB to DocumentDB by just changing the connection string, at least in the case of somewhat straightforward apps.
If you want to learn the ropes and get the hang of DocumentDB, then you should try the appropriately-named DocumentDB Emulator. In just a few words, this app allows you to test the functionality of the DocumentDB service. It includes support for creating JSON documents, support for queries, scaling collections and executing stored procedures.

Getting started with DocumentDB Emulator

Subsequent to its uneventful installation process, you will notice that it integrates with the taskbar. Use this compact menu to launch the Data Explorer in your computer's default browser. Once the emulator is up and running, you can start creating collections and thoroughly manage all your documents without writing code.
Please note that you can make use of any supported DocumentDB SDK or even use the DocumentDB REST API. More information about getting the most out of this NoSQL local emulator for DocumentDB can be found here or within the app's actual web-based UI, under the "Learn more about DocumentDB."
https://docs.microsoft.com/en-us/azure/documentdb/documentdb-nosql-local-emulator

Develop and test your apps locally for free, without Internet access and without needing Azure subscription

All in all, DocumentDB Emulator is a comprehensive and very useful app specially designed to offer users a very convenient way to learn the basics of DocumentDB, within a high-fidelity environment.
As expected, due to its nature, it does come with a few limitations, for instance, it does not support large numbers of collections, it cannot simulate DocumentDB consistency levels or multi-region replication, and, evidently, it's not a scalable service.