I'm currently working on a circular pane and am in the phase of writing tests. For optimalisation the layout does some (cached) calculations in the computePrefWidth, because, after all, how can a node be laid out if its container does not know what its min and pref sizes are? This works perfectly for all the trials I've written, putting the pane directly into the scene, or part of other panes.
But in the test (using TestFX) the layoutChildren() is called without ever calling computeMin/PrefWidth... Does that make sense? Tom