Unit testing with `codecov`

[SteveViss]

1. Covering all functions with testthatpackage by (at least) testing the class and structure of the output (@SteveViss or the author can take care of this part, see http://r-pkgs.had.co.nz/tests.html)
2. Functions should be tested to see if results make sense and/or is accurate (this task will be assignees to the author of the function).

[SteveViss]

Unit testing on as.alienData():

• Use @ibartomeus data and compare output of the function as.alienData() with the ./data/bartomeus2017.RData