Added extra test for unit with only base in model
Added extra test for unit with only base in model

nickerso/libcellml,MichaelClerx/libcellml,hsorby/libcellml,MichaelClerx/libcellml,cellml/libcellml,hsorby/libcellml,MichaelClerx/libcellml,cellml/libcellml,nickerso/libcellml,hsorby/libcellml,cellml/libcellml,nickerso/libcellml,nickerso/libcellml,cellml/libcellml,hsorby/libcellml