### Question:
JpaGroupRepository implements GroupRepository { @Override public Group get(String id) { long primaryKey = Long.parseLong(id); return manager.find(JpaGroup.class, primaryKey); }  @Override Class<? extends Group> getType(); @Override Group get(String id); @Override List<Group> getAll(); @Override List<Group> getLimitedList(int offset, int limit); @Override int getCountAll(); @Override Group save(Group item); @Override void delete(Group item); @Override Group findByTitle(String title);  }### Answer:
@Test public void getById_validId() { Group group = repository.get(GROUP_ID.toString()); assertThat(group, notNullValue()); assertThat(group.getTitle(), is(equalTo(GROUP_TITLE))); assertThat(group.getMemberIds().get(0), equalTo("1")); assertThat(group.getMemberIds().get(1), equalTo("5")); }
@Test public void getById_invalidId() { Group group = repository.get(INVALID_GROUP_ID); assertThat(group, is(nullValue())); }