### Question:
ExpressionEditorColumnRenderer extends BaseGridColumnRenderer<Optional<BaseExpressionGrid<? extends Expression, ? extends GridData, ? extends BaseUIModelMapper>>> { @Override public Group renderCell(final GridCell<Optional<BaseExpressionGrid<? extends Expression, ? extends GridData, ? extends BaseUIModelMapper>>> cell, final GridBodyCellRenderContext context) { if (cell == null || cell.getValue() == null) { return null; } final Group g = GWT.create(Group.class); if (cell.getValue() != null && cell.getValue() instanceof ExpressionCellValue) { final ExpressionCellValue ecv = (ExpressionCellValue) cell.getValue(); ecv.getValue().ifPresent(editor -> { g.add(editor.setX(editor.getPadding()).setY(editor.getPadding())); registry.register(editor); }); } return g; } ExpressionEditorColumnRenderer(final GridWidgetRegistry registry); @Override Group renderCell(final GridCell<Optional<BaseExpressionGrid<? extends Expression, ? extends GridData, ? extends BaseUIModelMapper>>> cell,
                            final GridBodyCellRenderContext context);  }### Answer:
@Test public void testRenderCellNoDMNExpression() throws Exception { cell = new BaseGridCell<>(new BaseGridCellValue<>(Optional.of(widget))); renderer.renderCell(cell, context); verify(renderedGroup, never()).add(any()); }
@Test public void testRenderCellDMNExpression() throws Exception { cell = new BaseGridCell<>(new ExpressionCellValue(Optional.of(widget))); renderer.renderCell(cell, context); verify(renderedGroup).add(editorGroup); verify(registry).register(widget); }