### Question:
DefaultCategoryDataset extends AbstractDataset implements CategoryDataset, PublicCloneable, Serializable { @Override public int getColumnCount() { return this.data.getColumnCount(); } DefaultCategoryDataset(); @Override int getRowCount(); @Override int getColumnCount(); @Override Number getValue(int row, int column); @Override Comparable getRowKey(int row); @Override int getRowIndex(Comparable key); @Override List<Comparable> getRowKeys(); @Override Comparable getColumnKey(int column); @Override int getColumnIndex(Comparable key); @Override List<Comparable> getColumnKeys(); @Override Number getValue(Comparable rowKey, Comparable columnKey); void addValue(Number value, Comparable rowKey,
                         Comparable columnKey); void addValue(double value, Comparable rowKey,
                         Comparable columnKey); void setValue(Number value, Comparable rowKey,
                         Comparable columnKey); void setValue(double value, Comparable rowKey,
                         Comparable columnKey); void incrementValue(double value,
                               Comparable rowKey,
                               Comparable columnKey); void removeValue(Comparable rowKey, Comparable columnKey); void removeRow(int rowIndex); void removeRow(Comparable rowKey); void removeColumn(int columnIndex); void removeColumn(Comparable columnKey); void clear(); @Override boolean equals(Object obj); @Override int hashCode(); @Override Object clone();  }### Answer:
@Test public void testGetColumnCount() { DefaultCategoryDataset d = new DefaultCategoryDataset(); assertSame(d.getColumnCount(), 0); d.addValue(1.0, "R1", "C1"); assertSame(d.getColumnCount(), 1); d.addValue(1.0, "R1", "C2"); assertSame(d.getColumnCount(), 2); d.addValue(2.0, "R1", "C2"); assertSame(d.getColumnCount(), 2); d.setValue(null, "R1", "C2"); assertSame(d.getColumnCount(), 2); }