[Meta] Add unit tests to the package

[ALanguillaume]

Add unit tests to the package

How to contribute

1 - Make sure you have clone the package on your computer
2 - Checkout this issue and spot a function that has no unit tests yet
3 - Open an issue to add unit tests to that function
4 - Go back to your local {kobocruncher} and PULL ! to make sure to work from the latest version of main
5 - Create a new branch <number>-iissue-add-test-<function-name>
6 - Add a unit test
7 - Inflate and make sure the check is passing
8 - Make a commit
9 - Make a PR and assigned to Edouard
10 - When the PR is merged Edouard updates the list below

TODO list off all functions to add unit tests to

• app_kobocruncher
• kobo_anonymise
• kobo_clean
• kobo_cruncher
• kobo_data
• kobo_dico
• kobo_frame
• kobo_indicator
• kobo_likert
• kobo_prepare_form
• kobo_ridl
• label_choiceset
• label_varhint
• label_varname
• plot_correlation
• plot_header
• plot_integer
• plot_integer_cross
• plot_likert
• plot_select_multiple
• plot_select_multiple_cross
• plot_select_one
• plot_select_one_cross
• plot_text
• template_1_exploration