add test for fieldmap
add test for fieldmap

shoshber/fmriprep,oesteban/fmriprep,poldracklab/fmriprep,poldracklab/fmriprep,poldracklab/fmriprep,chrisfilo/fmriprep,poldracklab/preprocessing-workflow,oesteban/preprocessing-workflow,oesteban/fmriprep,poldracklab/preprocessing-workflow,shoshber/fmriprep,oesteban/fmriprep,oesteban/preprocessing-workflow