Increase test coverage from 65% to 95-100%

[aanthonymax]

We need to finish the tests taking into account the existing ones. Everything is ready for finishing, we just need to sit over the work for a few more days. This task also includes this task #14

Files here - https://github.com/hmpl-language/hmpl/blob/main/test

The tests can be checked with the following command:

npm run test:watch

Useful links when working with tests:

https://hmpl-lang.dev/request.html#method
https://hmpl-lang.dev/examples.html