Add nf-core style testing suite for the Nextflow side of the code

[madeline-scyphers]

The NF code doesn't have a testing suite should. https://github.com/nf-core and https://nf-co.re/docs/guidelines/pipelines/recommendations/testing has some good resources on testing NF. We might want to add nf-core as as dev dependency. nf-core/nf-core plugins have a lot of NF specific tools.