### Question:
InvocationColumnExpressionHeaderMetaData extends EditableTextHeaderMetaData<TextBox, TextBoxDOMElement> implements HasCellEditorControls,
                                                                                                                                HasListSelectorControl { @Override public Optional<String> getPlaceHolder() { return placeHolder; } InvocationColumnExpressionHeaderMetaData(final Supplier<String> titleGetter,
                                                    final Consumer<String> titleSetter,
                                                    final SingletonDOMElementFactory<TextBox, TextBoxDOMElement> factory,
                                                    final Optional<String> placeHolder,
                                                    final ListSelectorView.Presenter listSelector,
                                                    final BiFunction<Integer, Integer, List<HasListSelectorControl.ListSelectorItem>> listSelectorItemsSupplier,
                                                    final Consumer<HasListSelectorControl.ListSelectorItem> listSelectorItemConsumer); @Override Group render(final GridHeaderColumnRenderContext context,
                        final double blockWidth,
                        final double blockHeight); @Override Optional<String> getPlaceHolder(); @Override Optional<Editor> getEditor(); @Override List<ListSelectorItem> getItems(final int uiRowIndex,
                                           final int uiColumnIndex); @Override void onItemSelected(final ListSelectorItem item);  }### Answer:
@Test public void testGetPlaceHolder() { assertThat(headerMetaData.getPlaceHolder()).isEqualTo(placeHolder); }