AllocatedSlot s6 = scheduler.scheduleImmediately(new ScheduledUnit(getTestVertex(Arrays.asList(first, third))));
assertEquals(second, s6.getInstance());
// release something on the first and second instance
s2.releaseSlot();
s6.releaseSlot();
AllocatedSlot s7 = scheduler.scheduleImmediately(new ScheduledUnit(getTestVertex(Arrays.asList(first, third))));
assertEquals(first, s7.getInstance());
assertEquals(1, scheduler.getNumberOfUnconstrainedAssignments());