### Question:
ColumnPermutation implements Serializable { @Override public String toString() { return columnIdentifiers.toString(); } 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 testToString() { final ColumnIdentifier expectedColumn1 = new ColumnIdentifier("table56", "column1"); final ColumnIdentifier expectedColumn2 = new ColumnIdentifier("table2", "column2"); final ColumnPermutation columnPermutation = new ColumnPermutation(expectedColumn1, expectedColumn2); final String expectedStringRepresentation = "[" + expectedColumn1.toString() + ", " + expectedColumn2.toString() + "]"; final String actualStringRepresentation = columnPermutation.toString(); assertEquals(expectedStringRepresentation, actualStringRepresentation); }