WorldCup (IASE, SS 26) - Assignment 2

A console-based Kotlin application that loads the 2026 FIFA World Cup group-stage data from a JSON file and lets the user view standings, list matches, place bets on individual matches, and check how many predictions were correct.

This assignment has two parts:

1. Fix the flaky tests — five tests in this project are intentionally flaky. Find them, explain why they fail intermittently, and fix the root cause.
2. Implement the stubs — three methods in BettingService and their tests in BettingServiceTest are left intentionally empty. Fill in both the production code and the test bodies.

Prerequisites

• JDK 25. The Gradle build requests this via toolchains, so any JDK that Gradle can locate or auto-provision will do; there is no need to set JAVA_HOME manually.
• No separate Gradle install is needed; the included Gradle wrapper (./gradlew) takes care of it.
• Recommended IDE: IntelliJ IDEA. VS Code with Kotlin extensions also works.

Project layout

src/main/kotlin/de/seuhd/worldcup/
    Main.kt                     Entry point and menu loop
    Console.kt                  Small input helpers (readInt, waitForEnter, ...)
    Data.kt                     @Serializable data classes mirroring the JSON schema
    JsonLoader.kt               Loads the bundled JSON resource from the classpath
    StandingsService.kt         Builds a sorted standings table for a group
    BettingService.kt           In-memory bet store and evaluation (contains stubs)
    FileBettingService.kt       File-backed bet store (used by the flaky tests)
src/main/resources/
    world_cup_2026_full_data.json   Tournament data (groups + knockouts)
src/test/kotlin/de/seuhd/worldcup/
    WorldCupTest.kt             Logic tests for standings and betting
    FileBettingServiceTest.kt   Tests against FileBettingService (contains flaky tests)
    BettingServiceTest.kt       Tests for the stub methods (bodies left empty for you)

Build, run, test

From the project root:

./gradlew build       # compile + test
./gradlew test        # tests only
./gradlew run         # start the interactive console
./gradlew repeatTests # run the test suite 20 times to surface flaky tests

In IntelliJ: File > Open the project root, let Gradle import finish, then run Main.kt from the gutter, or use the Gradle tool window to invoke application > run.

Part 1: Fix the flaky tests

There are five intentionally flaky tests in this project. ./gradlew test may pass on a given run, fail on another, or fail with a different combination of tests each time. Use ./gradlew repeatTests (20 runs) to get a reliable picture.

For each flaky test you should:

1. Reproduce the failure and convince yourself you understand the root cause.
2. Fix the production code, the test, or both, whichever is actually wrong. A fix that pins test execution order or wraps the assertion in a retry does not count.
3. Verify with ./gradlew repeatTests that the suite is now stable across all 20 runs.

A short writeup of what was wrong and why your fix addresses the root cause is part of the deliverable.

Part 2: Implement the stubs

BettingService.kt contains three methods whose bodies are TODO(...). Implement them according to their KDoc comments:

Method	Description
evaluateBonus(matches)	Returns the total bonus score: 3 points for an exact score match, 1 point for a correct outcome only, 0 otherwise.
removeBet(matchId)	Removes the bet for the given match. Does nothing if no bet exists.
changeBet(bet)	Updates an existing bet. Throws IllegalArgumentException if no bet exists for that match.

BettingServiceTest.kt contains matching empty test methods. Fill in each test body so it actually verifies the described behaviour. Every test must contain at least one assert* call — a TODO(...) body is not a passing test.

Menu

1) Show Standings        - prints a single group's table (or all 12 if you press Enter)
2) Show Matches          - lists matches of a group, with score if the match was played
3) Place Bets            - iterates through one group's matches, asking for 1 / 2 / 0
4) Show Betting Score    - compares stored bets against the actual results
5) Exit

The bet codes follow the assignment text: 1 = home win, 2 = away win, 0 = draw.

Standings rules

• Win = 3 points, Draw = 1 point, Loss = 0 points.
• Tie-break: better goal difference, then more goals scored.
• Matches with null scores are unplayed and do not contribute to the table.

Data file

src/main/resources/world_cup_2026_full_data.json ships with the project and is loaded from the classpath, so the program runs from any working directory (IDE, ./gradlew run, or a packaged jar). The schema:

• tournament: tournament name.
• groups[]: each has name, teams[], and matches[]. Each match carries matchId, round, date, homeTeam/awayTeam (team IDs), homeScore/awayScore (null until played), and ground (venue name).
• knockouts[]: parsed for completeness but out of scope for this assignment.