Premier League Predictor: FastAPI & PostgreSQL — Chapter 9, Exercise 3
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TASK
Complete a full real season (enter results for all fixtures needed to
give every team a real record), call the relegation preview, create a
new season, and roll it over with three real promoted team names —
then confirm the new season's roster has exactly 20 teams: 17 real
survivors plus the 3 promoted teams.

SOLUTION

Steps to complete this exercise, using season_id 1 as the completed
old season:

1. Ensure season 1 has a real, played result entered (via
   PATCH /api/fixtures/{id}/result, Chapter 6) for enough fixtures that
   every one of its 20 SeasonTeam-registered teams has at least one
   real result on record, so GET /api/seasons/1/table returns a
   genuinely ranked table rather than a set of all-zero rows.

2. Call GET /api/seasons/1/relegation-preview and note the three team
   names it returns — these are the real bottom three by the actual
   standings.

3. Create a new, empty season:

   POST /api/seasons
   {"name": "2027/28", "start_date": "2027-08-01", "end_date": "2028-05-31", "is_current": true}

   Note its returned id (season_id 2, for this example).

4. Roll season 1 over into season 2 with three real promoted team
   names:

   POST /api/seasons/2/rollover-from/1
   {"promoted_teams": [
     {"team_name": "Leicester City", "short_name": "Leicester"},
     {"team_name": "Leeds United", "short_name": "Leeds"},
     {"team_name": "Southampton", "short_name": "Southampton"}
   ]}

5. Confirm the response is a list of exactly 20 Team objects.

6. Cross-check: none of the three team names returned by the relegation
   preview in step 2 should appear in the roster returned in step 5 —
   confirming they were genuinely excluded, not accidentally carried
   over. All three of the promoted team names from step 4 should
   appear in the roster, confirming they were correctly added.

One-sentence confirmation: the new season's roster contains exactly 20
teams — the 17 real survivors from season 1, correctly excluding the
three relegated teams identified by the preview, plus the 3 newly
promoted teams entered by name.

WHY THIS WORKS AS AN ANSWER
----------------------------
It walks through the complete real workflow end to end (playing out a
season, previewing relegation, creating an empty new season, rolling
it over), and closes with a real, verifiable cross-check confirming
both halves of the rule at once — the relegated three are genuinely
absent, and the promoted three are genuinely present — rather than only
checking the total count of 20.