### Question:
PLIBuilder { public List<TreeSet<String>> getDistinctSortedColumns() throws InputIterationException { if (columns == null) { columns = new ArrayList<>(); calculateUnpurgedPLI(); } List<TreeSet<String>> distinctSortedColumns = new LinkedList<>(); for (HashMap<String, LongArrayList> columnMap : columns) { if (columnMap.containsKey(null)) { columnMap.remove(null); } distinctSortedColumns.add(new TreeSet<>(columnMap.keySet())); } return distinctSortedColumns; } PLIBuilder(RelationalInput input);  PLIBuilder(RelationalInput input, boolean nullEqualsNull); List<PositionListIndex> getPLIList(); long getNumberOfTuples(); List<TreeSet<String>> getDistinctSortedColumns();  }### Answer:
@Test public void testGetDistinctSortedColumns() throws InputIterationException { List<TreeSet<String>> expectedDistinctSortedColumns = fixture.getExpectedDistinctSortedColumns(); List<TreeSet<String>> actualDistinctSortedColumns = builder.getDistinctSortedColumns(); assertEquals(expectedDistinctSortedColumns, actualDistinctSortedColumns); }