Rewrite specs to TS

[sidiousvic]

Tests are few and currently written in JS.

No better time to rewrite them to TS for a bit more robustness.

@nayelyrodarte I will do it this in the weekend (Jul 10-12), but me know if you wanna give it a try before. No pressure.

It's a good opportunity to learn TS and get familiar with testing in Phantom.