### Question:
LiteralExpressionPMMLColumnRenderer extends StringColumnRenderer { @Override protected boolean isPlaceHolderToBeShown(final GridCell<String> cell) { return cell != null && cell.getValue() != null && StringUtils.isEmpty(cell.getValue().getValue()) && cell.getValue().getPlaceHolder() != null; }    }### Answer:
@Test public void testShowPlaceHolder_WithNullCellWithNullPlaceHolder() { assertThat(renderer.isPlaceHolderToBeShown(null)).isFalse(); }
@Test public void testShowPlaceHolder_WithNullCellValueWithNullPlaceHolder() { assertThat(renderer.isPlaceHolderToBeShown(new BaseGridCell<>(null))).isFalse(); }
@Test public void testShowPlaceHolder_WithEmptyCellValueWithEmptyValueWithNullPlaceHolder() { assertThat(renderer.isPlaceHolderToBeShown(new BaseGridCell<>(new BaseGridCellValue<>("")))).isFalse(); }
@Test public void testShowPlaceHolder_WithNullEmptyCellValueWithNullValueWithNullPlaceHolder() { assertThat(renderer.isPlaceHolderToBeShown(new BaseGridCell<>(new BaseGridCellValue<>(null)))).isFalse(); }
@Test public void testShowPlaceHolder_WithEmptyCellValueWithEmptyValueWithPlaceHolder() { assertThat(renderer.isPlaceHolderToBeShown(new BaseGridCell<>(new BaseGridCellValue<>("", PLACEHOLDER)))).isTrue(); }
@Test public void testShowPlaceHolder_WithEmptyCellValueWithNullValueWithPlaceHolder() { assertThat(renderer.isPlaceHolderToBeShown(new BaseGridCell<>(new BaseGridCellValue<>(null, PLACEHOLDER)))).isTrue(); }