Add a test to test error messages for non-existant providers/variants
Add a test to test error messages for non-existant providers/variants

leaflet-extras/leaflet-providers,leaflet-extras/leaflet-providers,kyroskoh/leaflet-providers,tomhughes/leaflet-providers,ximex/leaflet-providers,ximex/leaflet-providers,kyroskoh/leaflet-providers,tomhughes/leaflet-providers