Add tests, use globals and simplify script

[Ramilito]

Is your feature request related to a problem? Please describe.

Need tests to trust PR:s
Simplify passing arguments around with globals
The script is responsible for pre-pending environment variable, do it in-app instead so it's testable

Describe the solution you'd like

Use lazy_static for globals
Use tests that calls the binary and validates the output

Describe alternatives you've considered

Not testing and implementing bugs