We will start testing the buttons on the navigation bar.

• tree: adds a new tree
  assertions:
  the length of treesArray should increase by 1
  a new tree with an empty node is added

• tree: deletes the current tree. When clicked, a dialogue will appear with 'Do you want to delete this tree?'. Upon clicking OK, the tree will be deleted
  assertions:
  the length of treesArray should decrease by 1
  the current tree should be removed (can be tested by seeing if the sentence still exists)

NOTE: (test deletion on 1 tree) if there is only 1 tree remaining, a dialogue will pop up, showing a message 'Sorry! You cannot delete the last tree. Add a new tree first, then delete this tree.' . The tree will not be deleted.

tags: opens a window containing POS tags and dependency relation labels.
assertions:
the tags container will be displayed as follows:

• if a config file was not uploaded, the container will only show 'POS tags' and 'Relation labels' headers.
• if a config file was uploaded, the container will have buttons for each tag and label
  when clicking on the button again, the tags container should be hidden

listing: a list of sentences of the trees

• if the conll file has no sentences above the trees (# text lines), the sentence will contain the tokens found in the tree
• if the conll file has sentences, they will be shown
  clicking on a sentence will take to the tree of that sentence