missing unit tests for some functions

[kelly-sovacool]

I recommend having at least some unit tests for every function, and especially so for user-facing functions. It is not necessary to have 100% code coverage, but having minimal tests for user-facing functions helps safe guard against accidentally introducing API-breaking changes.

From looking at the codecov reports, it appears several functions lack any unit tests. These include:

• from_dada
• from_phyloseq
• create_biom_header
• to_biom
• add_jervis_bardy
• get_ord_stat
• tacoplot_zoom
• tacoplot_venn
• tacoplot_venn_ly
• tacoplot_euler
• tacoplot_prevalences