### Question:
AddDistrictTeamKey implements Func1<List<DistrictRanking>, List<DistrictRanking>> { public AddDistrictTeamKey(String districtKey) { this.districtKey = districtKey; } AddDistrictTeamKey(String districtKey); @Override List<DistrictRanking> call(List<DistrictRanking> districtTeams);  }### Answer:
@Test public void testAddDistrictTeamKey() { List<DistrictRanking> teamList = new ArrayList<>(); teamList.add(mDistrictTeam); teamList = mKeyAdder.call(teamList); assertNotNull(teamList); assertEquals(teamList.size(), 1); assertEquals(teamList.get(0), mDistrictTeam); String expectedKey = DistrictTeamHelper.generateKey(mDistrictTeam.getTeamKey(), mDistrictKey); assertEquals(mDistrictTeam.getKey(), expectedKey); assertEquals(mDistrictTeam.getDistrictKey(), mDistrictKey); }