An important case in GeoSPARQL is to capture fragments of the input XML (GML) or JSON (GeoJSON) as literals with custom datatypes: geo:gmlLiteral, geo:geoJSONLiteral.
This happens when converting eg GML, CityGML; and JSON-FG, CityJSON to RDF.

I think this is easy with RML, but I just want to be sure. Is it possible to add test cases for it?

I faced that problem recently, so I wrote some issues for different tools:

• how to "retype" rdf:JSON to geo:geoJSONLiteral? w3c/json-ld-syntax#425
• How to capture piece of XML to a literal as is? SPARQL-Anything/sparql.anything#452
• How to capture piece of XML to a literal as is? semantalytics/xsparql#38