decky/packages/practice_engine/test/weighted_selector_test.dart

import 'package:test/test.dart';
import 'package:practice_engine/models/question.dart';
import 'package:practice_engine/algorithms/weighted_selector.dart';

void main() {
  group('WeightedSelector', () {
    test('selects correct number of questions', () {
      final selector = WeightedSelector(seed: 42);
      final questions = List.generate(10, (i) {
        return Question(
          id: 'q$i',
          prompt: 'Question $i',
          answers: ['A', 'B'],
          correctAnswerIndices: [0],
          priorityPoints: i,
        );
      });

      final selected = selector.selectQuestions(
        candidates: questions,
        count: 5,
        currentAttemptIndex: 0,
      );

      expect(selected.length, equals(5));
    });

    test('returns all questions if count >= candidates length', () {
      final selector = WeightedSelector(seed: 42);
      final questions = List.generate(5, (i) {
        return Question(
          id: 'q$i',
          prompt: 'Question $i',
          answers: ['A', 'B'],
          correctAnswerIndices: [0],
        );
      });

      final selected = selector.selectQuestions(
        candidates: questions,
        count: 10,
        currentAttemptIndex: 0,
      );

      expect(selected.length, equals(5));
    });

    test('returns empty list for empty candidates', () {
      final selector = WeightedSelector(seed: 42);
      final selected = selector.selectQuestions(
        candidates: [],
        count: 5,
        currentAttemptIndex: 0,
      );

      expect(selected, isEmpty);
    });

    test('returns empty list for count <= 0', () {
      final selector = WeightedSelector(seed: 42);
      final questions = List.generate(5, (i) {
        return Question(
          id: 'q$i',
          prompt: 'Question $i',
          answers: ['A', 'B'],
          correctAnswerIndices: [0],
        );
      });

      final selected = selector.selectQuestions(
        candidates: questions,
        count: 0,
        currentAttemptIndex: 0,
      );

      expect(selected, isEmpty);
    });

    test('no duplicates in selection', () {
      final selector = WeightedSelector(seed: 42);
      final questions = List.generate(10, (i) {
        return Question(
          id: 'q$i',
          prompt: 'Question $i',
          answers: ['A', 'B'],
          correctAnswerIndices: [0],
          priorityPoints: 5,
        );
      });

      final selected = selector.selectQuestions(
        candidates: questions,
        count: 5,
        currentAttemptIndex: 0,
      );

      final ids = selected.map((q) => q.id).toSet();
      expect(ids.length, equals(selected.length));
    });

    test('higher priority questions are more likely to be selected', () {
      final selector = WeightedSelector(seed: 42);
      final questions = [
        Question(
          id: 'low',
          prompt: 'Low priority',
          answers: ['A', 'B'],
          correctAnswerIndices: [0],
          priorityPoints: 1,
        ),
        Question(
          id: 'high',
          prompt: 'High priority',
          answers: ['A', 'B'],
          correctAnswerIndices: [0],
          priorityPoints: 100,
        ),
      ];

      // Run multiple selections and count occurrences
      int highSelected = 0;
      for (int i = 0; i < 100; i++) {
        final selected = selector.selectQuestions(
          candidates: questions,
          count: 1,
          currentAttemptIndex: 0,
        );
        if (selected.first.id == 'high') {
          highSelected++;
        }
      }

      // High priority should be selected more often
      expect(highSelected, greaterThan(50));
    });
  });
}