### Question:
IdFieldEmittableKey extends EmittableKey { public Text getIdField() { return super.getFieldName(); } IdFieldEmittableKey();  IdFieldEmittableKey(final String mongoFieldName); Text getIdField(); Text getId(); void setId(final Text value); @Override void readFields(DataInput data); @Override void write(DataOutput data); @Override String toString(); @Override BSONObject toBSON(); @Override int hashCode(); @Override boolean equals(Object obj); @Override int compareTo(EmittableKey other);  }### Answer:
@Test public void testGetIdField() { IdFieldEmittableKey key = new IdFieldEmittableKey("test.id.key.field"); assertEquals(key.getIdField().toString(), "test.id.key.field"); }