Improve test coverage for encode.ts file

[lukasbicus]

Current improvement:

Hi @xseman. Please check the implementation. The main change is, that I have introduced the EncodeError class with the EncodeErrorMessage enum. What do you think about that approach?

[xseman]

If you prefer using EncodeError instead of a plain Error, that's fine with me. The main goal for increasing coverage is to test the untested branching logic.

I'm aiming for about 90% branch coverage per file, but any improvement is great! It might not be possible to increase it further because reports are still experimental. If you think we've hit the limit, I'm happy with the PR as is.

[lukasbicus]

@xseman - I asked because this can lead to a major breaking change. On the other hand, I see an added value in creating an enum of errors and moving the changing parts of error response to extensions. It's much easier to process that structure on a frontend. I will continue with the encode.ts file. I believe I will reach 100% coverage or near.

[lukasbicus]

[xseman]

Nice, it looks like you've handled everything with the encoding. If you're not working on decoding, we can merge it.

[lukasbicus]

I have assigned some time for bysquere on Friday. So this can be merged and I will open another PR or I can continue within this one on Friday.