Added new unit tests for `fb206ec`.

test/mu/compare/Makefile

.../compare/expected-fi-digital-emptyassignment-lualatex.pdf

.../compare/expected-fi-digital-emptyassignment-pdflatex.pdf

.../mu/compare/expected-fi-digital-noassignment-lualatex.pdf

.../mu/compare/expected-fi-digital-noassignment-pdflatex.pdf

...u/compare/expected-fi-digital-someassignment-lualatex.pdf

...u/compare/expected-fi-digital-someassignment-pdflatex.pdf

.../compare/expected-fi-printed-emptyassignment-lualatex.pdf

.../compare/expected-fi-printed-emptyassignment-pdflatex.pdf

.../mu/compare/expected-fi-printed-noassignment-lualatex.pdf

.../mu/compare/expected-fi-printed-noassignment-pdflatex.pdf

...e/expected-fi-printed-someassignment-oneside-lualatex.pdf

...e/expected-fi-printed-someassignment-oneside-pdflatex.pdf

...e/expected-fi-printed-someassignment-twoside-lualatex.pdf

...e/expected-fi-printed-someassignment-twoside-pdflatex.pdf

test/mu/compare/fi-digital-emptyassignment.tex

test/mu/compare/fi-digital-noassignment.tex

test/mu/compare/fi-digital-someassignment.tex

test/mu/compare/fi-printed-emptyassignment.tex

test/mu/compare/fi-printed-noassignment.tex