assert root.descriptor.displayName == 'Run build'
    }

    boolean isEmpty() {
        assertHasZeroOrMoreTrees()
        return events.empty
    }

    /**
     * Returns all events, in the order received.
     */
    List<ProgressEvent> getAll() {
        assertHasZeroOrMoreTrees()
        return events
    }

    /**
     * Returns all operations, in the order started.
     */