Premier League Predictor: Django & MySQL — Chapter 9, Exercise 3
====================================================

TASK
Complete a full real season (enter results for enough fixtures to give
every team a real record), call relegation_preview, create a new
empty Season in the admin, call rollover_survivors, confirm the new
season has exactly 17 SeasonTeam rows, then add 3 promoted teams via
SeasonTeamInline (using the "+" popup for at least one genuinely new
team) and confirm the new season's roster reaches exactly 20.

SOLUTION

Using old_season_id 1 (2026/27, fully completed) and a freshly created
new_season_id 2 (2027/28, no SeasonTeam rows yet):

1. Enter results for enough fixtures via enter_result that every one
   of the 20 teams in season 1 has at least a partial real record —
   compute_league_table depends only on played fixtures existing, not
   a fully finished 38-gameweek season, so a handful of results per
   team is enough for this exercise.

2. GET /seasons/1/relegation-preview/:

   [
     {"id": 18, "name": "Sheffield United", "short_name": "SHU"},
     {"id": 19, "name": "Luton Town", "short_name": "LUT"},
     {"id": 20, "name": "Burnley", "short_name": "BUR"}
   ]

   These are the three teams currently sitting bottom of season 1's
   real table, per its own points/goal-difference/goals-for ordering.

3. In the admin, create a new Season named "2027/28" with is_current
   left False for now (id 2). No SeasonTeam rows exist for it yet.

4. POST /seasons/2/rollover-survivors-from/1/:

   {
     "new_season_id": 2,
     "survivors_carried_forward": 17,
     "next_step": "Add the 3 promoted teams via the Season admin
       page's own SeasonTeamInline"
   }

   Checking SeasonTeam.objects.filter(season_id=2).count() in the
   shell now returns 17 — every team from season 1's table except
   Sheffield United, Luton Town, and Burnley (the three names returned
   by relegation_preview in step 2).

5. Open the new Season (id 2) in the admin. Its SeasonTeamInline shows
   the 17 survivors already present, and correctly still allows up to
   3 more rows before max_num=20/validate_max=True blocks any further
   addition.

6. Add the 3 promoted teams: "Leicester City" (an existing Team row
   from a previous season, found via the ordinary autocomplete
   search), "Ipswich Town" (also existing), and "Real Newco FC" (a
   genuinely brand-new club with no existing Team row at all, added
   via the "+" popup next to the team autocomplete field, which opens
   a small form to create the Team on the spot without leaving the
   Season admin page). Save the inline.

7. SeasonTeam.objects.filter(season_id=2).count() now returns 20 —
   the 17 survivors plus the 3 just added — and a 21st attempted
   addition on this same inline is rejected by validate_max=True,
   confirming the cap still holds even after being reached through
   two different mechanisms (the automated rollover and the manual
   admin entries) rather than just one.

WHY THIS WORKS AS AN ANSWER
----------------------------
It walks the full real sequence end to end — preview, create, roll
over the mechanical part, then complete the human part through the
admin, including the specific "+" popup case the task calls for — and
confirms the row counts at each stage (17 after rollover, 20 after
the admin additions), tying the result directly back to both the
relegation_preview's own returned team names and the max_num cap
established in Chapter 3.