Test utils: print error numbers using the optimal width.
Test utils: print error numbers using the optimal width.

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