assertEquals(13.34112, branchPart.collectFreeEnergy().doubleValue(), 0.000001);
// can not collect the free energy more than once
assertEquals(new BigDecimal(0), branchPart.collectFreeEnergy());
int nbFall = 0;
for (ObservableTestHelper observerHelper : observerHelpers) {
if (observerHelper.nbUpdated() == 4) {
// the single falling leaf (the first one)
assertEquals(LeafUpdateCode.age, observerHelper.getUpdateObjects().get(0));
assertEquals(LeafUpdateCode.efficiency, observerHelper.getUpdateObjects().get(1));
assertEquals(LeafUpdateCode.energy, observerHelper.getUpdateObjects().get(2));
assertEquals(LeafUpdateCode.fall, observerHelper.getUpdateObjects().get(3));