Premier League Predictor: Astro — Chapter 9, Exercise 3
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TASK
Set up a complete 20-team season with a full league table, call
GET /api/seasons/{seasonId}/relegation-preview to confirm the correct
bottom three, then call POST /api/seasons/{seasonId}/rollover against
a newly created next season and confirm the new season's season_teams
contains exactly the 17 survivors — followed by three calls to
Chapter 3's own POST /api/seasons/{id}/teams route to add three
promoted clubs, bringing the new season back up to 20.

SOLUTION

Steps to complete the hands-on part:

1. Using Chapters 2-4, create a season ("2026/27"), add 20 real teams
   to it, create 38 gameweeks' worth of fixtures (or a smaller
   representative set, so long as every team has at least one played
   fixture and the table has no genuinely tied positions right at the
   17/18 boundary, to keep the bottom-three cutoff unambiguous), and
   enter real results for all of them via Chapter 6's own
   PATCH /api/fixtures/{id}/result route.
2. Call GET /api/seasons/{seasonId}/table (Chapter 7) and note the
   bottom three teams by name.
3. Call GET /api/seasons/{seasonId}/relegation-preview. Confirm its
   own "relegated" array lists exactly those same three teams, in the
   same order, and its "survivors" array lists the other 17.
4. Create a new season, "2027/28", via POST /api/seasons.
5. Call POST /api/seasons/{oldSeasonId}/rollover with
   { "new_season_id": <2027/28's id> }.
6. Query season_teams directly for the new season:
   SELECT t.name FROM season_teams st
   JOIN teams t ON t.id = st.team_id
   WHERE st.season_id = <2027/28's id>;
   Confirm this returns exactly the 17 survivor names from Step 3 —
   no more, no fewer, and none of the three relegated teams present.
7. Call POST /api/seasons/{2027/28 id}/teams three times, once per
   promoted club, e.g.:
   { "team_name": "Leeds United", "short_name": "Leeds" }
   { "team_name": "Sunderland", "short_name": "Sunderland" }
   { "team_name": "Sheffield United", "short_name": "Sheff Utd" }
8. Re-run the same SELECT from Step 6. Confirm the new season now has
   exactly 20 teams: the original 17 survivors plus the three
   promoted clubs just added.

Confirm one more detail directly: the three relegated teams' own
season_teams rows for the OLD season are still present and unchanged
— querying season_teams for the old season_id should still return all
20 original teams, proving relegation never deleted anything from the
old season's own historical record.

WHY THIS WORKS AS AN ANSWER
----------------------------
It completes the real, hands-on setup for a full season and confirms
every step of the chapter's own real workflow against actual data:
the relegation preview matching the league table's own bottom three
exactly, the rollover producing precisely 17 new rows with none of
the relegated teams present, the three promoted teams correctly
bringing the new season back to a full 20 via Chapter 3's own
unmodified route, and — the detail most worth explicitly checking —
confirmation that the old season's own season_teams rows are entirely
untouched, proving relegation really is an omission from the new
season rather than a deletion from the old one.