### Question:
ColumnIdentifier implements Comparable<ColumnIdentifier>, Serializable { @Override public String toString() { if (this.tableIdentifier.isEmpty() && this.columnIdentifier.isEmpty()) return ""; return tableIdentifier + TABLE_COLUMN_CONCATENATOR + columnIdentifier; } ColumnIdentifier();  ColumnIdentifier(String tableIdentifier, String columnIdentifier); String getTableIdentifier(); void setTableIdentifier(String tableIdentifier); String getColumnIdentifier(); void setColumnIdentifier(String columnIdentifier); @Override String toString(); String toString(Map<String, String> tableMapping, Map<String, String> columnMapping); static ColumnIdentifier fromString(Map<String, String> tableMapping, Map<String, String> columnMapping, String str); @Override int hashCode(); @Override boolean equals(Object obj); @Override int compareTo(ColumnIdentifier other); static final String TABLE_COLUMN_CONCATENATOR; static final String TABLE_COLUMN_CONCATENATOR_ESC; }### Answer:
@Test public void testToString() { String tableIdentifier = "table1"; String columnIdentifier = "column1"; ColumnIdentifier identifier = new ColumnIdentifier(tableIdentifier, columnIdentifier); String expectedIdentifier = tableIdentifier + "." + columnIdentifier; String actualIdentifier = identifier.toString(); assertEquals(expectedIdentifier, actualIdentifier); }