You will need to download the correct .jar file drivers for the connection (you need to determine what version of cosmos your are trying to connect to) - try here https://www.cdata.com/drivers/cosmosdb/jdbc/ to pick up the driver files you need. You need to add in the driver files to ReadyAPI!/bin/ext directory in your program files directory (e.g. C:\Program Files\SmartBear\ReadyAPI-2.5.0\bin\ext)
You will then need to edit the JDBC preferences adding the appropriate jdbc connection - see the photo
In the Driver field - input the following: CosmosDBDriver/cdata.jdbc.cosmosdb.CosmosDBDriver
In the Connection field input you need to add the following:
One other thing - you will need to ensure the version of Java you are using for your runtime is correct relative to the .jar files you are using a device drivers for the connection. I'm assuming you already have JRE or JDK installed. there is a reason (that I cant remember) that may impact you - even though you just need runtime files - grab the JDK anyway - it has an extended set - there is a reason why you should grab the JDK rather than the JRE - I just cant remember what it is.