### Question:
ColumnPermutation implements Serializable { public List<ColumnIdentifier> getColumnIdentifiers() { return columnIdentifiers; } ColumnPermutation();  ColumnPermutation(ColumnIdentifier... columnIdentifier); List<ColumnIdentifier> getColumnIdentifiers(); void setColumnIdentifiers(List<ColumnIdentifier> identifiers); @Override String toString(); String toString(Map<String, String> tableMapping, Map<String, String> columnMapping); static ColumnPermutation fromString(Map<String, String> tableMapping, Map<String, String> columnMapping, String str); @Override int hashCode(); @Override boolean equals(Object obj);  }### Answer:
@Test public void testGetColumnIdentifiers() { final ColumnIdentifier expectedColumn1 = new ColumnIdentifier("table1", "column1"); final ColumnIdentifier expectedColumn2 = new ColumnIdentifier("table2", "column2"); final ColumnIdentifier expectedColumn3 = new ColumnIdentifier("table3", "column3"); final ColumnPermutation columnPermutation = new ColumnPermutation(expectedColumn2, expectedColumn3, expectedColumn1); final List<ColumnIdentifier> actualColumnIdentifiers = columnPermutation.getColumnIdentifiers(); assertTrue(3 == actualColumnIdentifiers.size()); assertTrue(actualColumnIdentifiers.get(0).equals(expectedColumn2)); assertTrue(actualColumnIdentifiers.get(1).equals(expectedColumn3)); assertTrue(actualColumnIdentifiers.get(2).equals(expectedColumn1)); }