Improve test case.
Improve test case.

Add empty string literal to concatenation test.

MathieuDuponchelle/meson,MathieuDuponchelle/meson,jpakkane/meson,jpakkane/meson,jeandet/meson,pexip/meson,pexip/meson,jpakkane/meson,becm/meson,mesonbuild/meson,pexip/meson,jpakkane/meson,pexip/meson,MathieuDuponchelle/meson,mesonbuild/meson,becm/meson,jeandet/meson,becm/meson,MathieuDuponchelle/meson,thiblahute/meson,pexip/meson,becm/meson,becm/meson,MathieuDuponchelle/meson,mesonbuild/meson,becm/meson,QuLogic/meson,QuLogic/meson,QuLogic/meson,jpakkane/meson,mesonbuild/meson,jpakkane/meson,thiblahute/meson,QuLogic/meson,becm/meson,MathieuDuponchelle/meson,mesonbuild/meson,QuLogic/meson,pexip/meson,mesonbuild/meson,MathieuDuponchelle/meson,thiblahute/meson,jeandet/meson,jpakkane/meson,mesonbuild/meson,pexip/meson,QuLogic/meson,QuLogic/meson,QuLogic/meson,jeandet/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,jeandet/meson,jeandet/meson,becm/meson,thiblahute/meson,jeandet/meson,thiblahute/meson,jpakkane/meson,becm/meson,mesonbuild/meson,thiblahute/meson,thiblahute/meson,pexip/meson,becm/meson,pexip/meson,jeandet/meson,thiblahute/meson,MathieuDuponchelle/meson,MathieuDuponchelle/meson,jpakkane/meson,jeandet/meson,QuLogic/meson,thiblahute/meson