Add a REPL test

[SuperFola]

Is your feature request related to a problem?

The repl can break without us noticing, because it is interactive by nature.

Describe the solution you would like

I’d like to be able to test the repl without having to type anything.

The bare minimum should be to test that text can be inputted.

If possible I’d like to test completion and colors too.

Is it a big modification to the language? Leave it if you don't know

• [ ] Breaking change
• [ ] Compiler/syntax modifications
• [ ] Runtime modifications (standard library, modules, packages...)