### Question:
MatrixSeries extends Series implements Serializable { public int getItemRow(int itemIndex) { return itemIndex / getColumnsCount(); } MatrixSeries(String name, int rows, int columns); int getColumnsCount(); Number getItem(int itemIndex); int getItemColumn(int itemIndex); @Override int getItemCount(); int getItemRow(int itemIndex); int getRowCount(); double get(int i, int j); void update(int i, int j, double mij); void zeroAll(); @Override boolean equals(Object obj);  }### Answer:
@Test public void testGetItemRow() { MatrixSeries m = new MatrixSeries("Test", 3, 2); assertEquals(0, m.getItemRow(0)); assertEquals(0, m.getItemRow(1)); assertEquals(1, m.getItemRow(2)); assertEquals(1, m.getItemRow(3)); assertEquals(2, m.getItemRow(4)); assertEquals(2, m.getItemRow(5)); }