Add tests

[grabbou]

What to test and how

[czystyl]

I started thinking how we can test

[guilhermedecampo]

@czystyl can you share your ideas? Looking forward to helping!

[knowbody]

here are some neat and simple examples: https://github.com/jthegedus/reasonml

@guilhermedecampo that would be awesome!

[czystyl]

@knowbody I did the same on my branch - that is simple jest tests.
@guilhermedecampo You can check branch test/init there is some initial setup for tests.

What issues in on test/init branch:

• The test code needs to be compiled before jest command: ReasonMl -> js -> jest. It not a good DX.
• needs to figurate how to render Reason component inside tests and create the snapshots. Check what is wrong with snapshots here: https://reasonml.chat/t/snapshot-testing-a-reasonreact-component/249

[guilhermedecampo]

thank you guys! Checking soon.

[knowbody]

ok changing the topic of this, let's add, instead of just thinking about tests ;p

@Czysty if you have anything, please send a WIP PR so we can start with something and then we'll improve it