Add getUnits to increase coverage.
Add getUnits to increase coverage.

libcellml/buildbot-testing,MichaelClerx/libcellml,cellml/libcellml,nickerso/libcellml,hsorby/libcellml,nickerso/libcellml,MichaelClerx/libcellml,libcellml/buildbot-testing,hsorby/libcellml,nickerso/libcellml,cellml/libcellml,hsorby/libcellml,hsorby/libcellml,cellml/libcellml,MichaelClerx/libcellml,cellml/libcellml,nickerso/libcellml