DefaultTableModel tm = new DefaultTableModel(2, 3);
tm.setColumnIdentifiers(new String[] {"C0", "C1", "C2"});
JTable table = new JTable(tm);
table.setAutoCreateColumnsFromModel(false);
DefaultTableColumnModel tcm1 = new DefaultTableColumnModel();
tcm1.addColumn(new TableColumn(1, 50));
table.setColumnModel(tcm1);
table.setAutoCreateColumnsFromModel(true);
TableColumnModel tcm2 = table.getColumnModel();
harness.check(tcm2.getColumnCount(), 3);