[WIP] Test directives

 - [ ] Write tests for dropper
 - [x] Write tests for overlay
 - [ ] Write tests for repository
 - [ ] Write tests for draggable
 - [ ] Write tests for droppable
 - [ ] Write tests for focus-me
 - [ ] Write tests for navbar-item
 - [ ] Write tests for property-value
 - [ ] Write tests for tree-node
 - [ ] Write tests for tree