Added tests to confirm no redefinition of units for identical imports
Added tests to confirm no redefinition of units for identical imports

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