Java
    Java HashMap backed implementation of ReadableMap and WritableMap Instances of this class SHOULD NOT be used for communication between java and JS, use instances of WritableNativeMap created via Arguments#createMap or just ReadableMap interface if you want your "native" module method to take a map from JS as an argument.
Main purpose for this class is to be used in java-only unit tests, but could also be used outside of tests in the code that operates only in java and needs to communicate with RN modules via their JS-exposed API.