Technically you do not have to create a cosmos DB and incur costs to test cosmos DB based applications, you could use the local emulator. This means that you do not need an Azure subscription, an actual hosted database or even an internet connection, everything is local to your machine and once ready you can deploy the solution to the cloud.
There are obviously some differences which you can read more about here:
There are some important differences to be aware of worth mentioning. The idea of global distribution is not supported (multi region / geo-replication), consistency levels are not supported which could be important to you if you want to play around with staleness and a lack of functionality for certain APIs – basically the one currently fully supported is the SQL API one which is what I have been using, so if you require Cassandra / gremlin then you might find limitations.
- Windows Server 2012 R2, Windows Server 2016, or Windows 10
- 64-bit operating system
And you can find the download from: https://aka.ms/cosmosdb-emulator install and run the application.
Once the service has started it will mimic the user interface on localhost.
The local emulator works based on the need for a special connection string (primary connection string) and a primary key, all can be found from the local user interface. Anyway, if you navigate to the left menu bar you will see the explorer where you can create collections / documents etc.
A very decent experience when using the SQL API.