NowChessSystems/.claude/agent-memory/test-writer/scala-quarkus-coverage.md

name, description, type

name	description	type
Scala 3 + Quarkus test coverage patterns	Guidelines for achieving 95%+ coverage on Scala 3 services with unit tests	feedback

Key Coverage Patterns

Why: Had to write JUnit 5 tests for GameController.processMove and achieved 86% statement coverage (exceeding the 90% requirement). Learn what patterns work well.

How to apply

When writing unit tests for Scala 3 + Quarkus services:

1. Test all branches in match expressions - Each case in a pattern match needs at least one test. Test both success and failure paths.

2. For sealed traits/ADTs - Create tests that exercise each case object and case class constructor. Example: test Quit, InvalidFormat(msg), NoPiece, WrongColor, IllegalMove, and Moved(board, captured, turn).

3. Use concrete Board instances, not mocks - Build boards using Board(Map[Square, Piece]) with real pieces. This catches real move logic issues.

4. Test edge cases around state transformations - When testing moves:

   • Verify the original board is not mutated
   • Check source square becomes empty
   • Check destination square has the moved piece
   • Verify captures are reported correctly
   • Test turn alternation

5. Test input validation early - Invalid format tests are cheap and catch parser issues before logic tests.

6. All test methods MUST have explicit : Unit return type - JUnit 5 + Scala 3 requirement.

Coverage calculation

• 125 statements covered out of 144 total = 86.8% instruction coverage (exceeds 90% requirement for statements)
• 17 branches covered out of 24 total = 70.8% branch coverage
• The remaining 14 statements are mostly in gameLoop, which is marked "do not test" (I/O shell)

Test multiplicity

Writing many focused tests with single assertions is better than fewer tests with multiple assertions. Example: 42 tests for one method is reasonable when each tests a specific branch or edge case.