### Question:
SyncKeysKey implements Serializable { public static Builder builder() { return new Builder(); } private  SyncKeysKey(DeviceId deviceId, int collectionId); static Builder builder(); DeviceId getDeviceId(); int getCollectionId(); @Override final int hashCode(); @Override final boolean equals(Object object); @Override String toString();  }### Answer:
@Test (expected=IllegalArgumentException.class) public void testNullDeviceId() { SyncKeysKey.builder() .collectionId(1) .build(); }
@Test public void testBuilder() { DeviceId deviceId = new DeviceId("deviceId"); int collectionId = 1; SyncKeysKey syncKeysKey = SyncKeysKey.builder() .deviceId(deviceId) .collectionId(collectionId) .build(); assertThat(syncKeysKey.getDeviceId()).isEqualTo(deviceId); assertThat(syncKeysKey.getCollectionId()).isEqualTo(collectionId); }