tests: add a text dy dx attribute sample.
tests: add a text dy dx attribute sample.

janmarthedal/mathml2svg,wavewave/lasem,janmarthedal/mathml2svg,gjtorikian/lasem,janmarthedal/mathml2svg,janmarthedal/mathml2svg,wavewave/lasem,wavewave/lasem,gjtorikian/lasem,gjtorikian/lasem,gjtorikian/lasem,wavewave/lasem