### Question:
DateColumn extends AbstractColumn<DateColumn, LocalDate> implements DateFilters,
        DateFillers<DateColumn>,
        DateMapFunctions,
        CategoricalColumn<LocalDate> { @Override public int countUnique() { IntSet ints = new IntOpenHashSet(size()); for (int i = 0; i < size(); i++) { ints.add(data.getInt(i)); } return ints.size(); } private  DateColumn(String name, IntArrayList data); static DateColumn create(final String name); static DateColumn createInternal(String name, int[] data); static DateColumn create(final String name, final int initialSize); static DateColumn create(String name, Collection<LocalDate> data); static DateColumn create(String name, LocalDate... data); static DateColumn create(String name, Stream<LocalDate> stream); @Override int size(); @Override DateColumn subset(final int[] rows); DateColumn appendInternal(int f); DateColumn set(int index, int value); @Override DateColumn set(int index, LocalDate value); void setPrintFormatter(DateTimeFormatter dateTimeFormatter, String missingValueString); void setPrintFormatter(DateTimeFormatter dateTimeFormatter); @Override String getString(int row); @Override String getUnformattedString(int row); @Override DateColumn emptyCopy(); @Override DateColumn emptyCopy(int rowSize); @Override DateColumn copy(); @Override void clear(); @Override DateColumn lead(int n); @Override DateColumn lag(int n); @Override void sortAscending(); @Override void sortDescending(); @Override int countUnique(); @Override DateColumn unique(); @Override DateColumn append(final Column<LocalDate> column); @Override DateColumn append(Column<LocalDate> column, int row); @Override DateColumn set(int row, Column<LocalDate> column, int sourceRow); @Override LocalDate max(); @Override LocalDate min(); @Override DateColumn set(Selection rowSelection, LocalDate newValue); @Override DateColumn appendMissing(); @Override LocalDate get(int index); @Override boolean isEmpty(); @Override IntComparator rowComparator(); @Override DateColumn append(LocalDate value); @Override DateColumn appendObj(Object obj); @Override DateColumn appendCell(String string); @Override DateColumn appendCell(String string, AbstractColumnParser<?> parser); @Override int getIntInternal(int index); @Override Table summary(); static boolean valueIsMissing(int i); @Override int countMissing(); List<LocalDate> top(int n); List<LocalDate> bottom(int n); IntIterator intIterator(); @Override DateColumn removeMissing(); @Override List<LocalDate> asList(); @Override DateColumn where(Selection selection); Set<LocalDate> asSet(); @Override boolean contains(LocalDate localDate); @Override DateColumn setMissing(int i); double[] asDoubleArray(); DoubleColumn asDoubleColumn(); @Override boolean isMissing(int rowNumber); double getDouble(int i); @Override int byteSize(); @Override byte[] asBytes(int rowNumber); @Override Iterator<LocalDate> iterator(); @Override DateColumn fillWith(Iterator<LocalDate> iterator); @Override DateColumn fillWith(Iterable<LocalDate> iterable); @Override DateColumn fillWith(Supplier<LocalDate> supplier); @Override LocalDate[] asObjectArray(); @Override int compare(LocalDate o1, LocalDate o2);  }### Answer:
@Test public void testCountUnique() { column1.append(LocalDate.of(2000, 1, 1)); column1.append(LocalDate.of(2000, 1, 1)); column1.append(LocalDate.of(2000, 2, 1)); column1.appendMissing(); assertEquals(3, column1.countUnique()); }