Scala test fw

First attempt to use the inhouse Scala testing framework with one test for checking the picture overlay functionality. Keep in mind that I am a beginner Scala dev so code will likely look very "Javaish"
What does this method do? I find it a little confusing because it sounds like a method that wouldn't mutate anything and would just return `true` or `false`, which if it did do so in this context, would do nothing.

If it is doing some kind of side-effect, you should probably give it a better name, and you should call it with parentheses.

```scala
picOverlay.checkIsDisplayed()
```