add more tests #48
Description
Add more tests here: https://github.com/lunduniversity/introprog-scalalib/tree/master/src/test/scala
The goal is to have at least one test per method for non-gui-related stuff. Currently, only the IO api is non-gui-related, so this issue means adding more tests on IO.
We use munit which wraps JUnit in a nice scala api.