Add coverage test to satisfy llvm coverage.
Add coverage test to satisfy llvm coverage.

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