Garbage Collection Test Failes

[maarzt]

Running the unit tests currently fails if the graphics environment is enabled. (Both on window and linux)

Running org.mastodon.model.ModelGarbageCollectionTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.33 sec

Results :

Failed tests: 
  testIfMastodonIsGarbageCollectable(org.mastodon.mamut.GarbageCollectionTest)

[maarzt]

I'm going to fix it.