test: unit tests for api layer

[mateo-ivc]

Description

Implemented unittests for api/columns.go

Changelog

api/columns_test.go

• Added tests for the various functions in api/columns.go

Checklist

• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [ ] The light- and dark-theme are both supported and tested
• [ ] The design was implemented and is responsive for all devices and screen sizes
• [x] The application was tested in the most commonly used browsers (e.g. Chrome, Firefox, Safari)

(Optional) Visual Changes