then:
        1 * listener.statusChanged({it.description == 'main'})
        1 * listener.statusChanged({it.description == 'nested'})

        when:
        adapter.onOperationEnd()
        adapter.onOperationEnd()

        then:
        1 * listener.statusChanged({it.description == 'main'})
        1 * listener.statusChanged({it.description == ''})
        0 * _._
    }

/**
 * DO NOT CHANGE THIS INTERFACE. It is part of the cross-version protocol.
 */
public interface ProgressListenerVersion1 {
    void onOperationStart(String description);

    void onOperationEnd();

        }

        @Override
        public void progress(ProgressEvent event) {
        }

        @Override
        public void completed(ProgressCompleteEvent event) {
            progressListener.onOperationEnd();
        }
    }

    @Override
    public void onOperationStart(final String description) {
        stack.addFirst(description == null ? "" : description);
        fireChangeEvent();
    }

    @Override
    public void onOperationEnd() {
        stack.removeFirst();
        fireChangeEvent();
    }

    private void fireChangeEvent() {
        final String description = stack.isEmpty() ? "" : stack.getFirst();

                progressListener.onOperationStart(startEvent.getDescription());
            } else if (event instanceof ProgressCompleteEvent) {
                progressListener.onOperationEnd();
            }
        }
    }