https://www.touilleur-express.fr/2021/02/08/scala-kata-01/

kata1.java

package code.kata.gildedrose;

import org.junit.jupiter.api.Test;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import static org.assertj.core.api.AssertionsForInterfaceTypes.assertThat;

class kata1Test {

    public static List<Integer> processSum(List<Integer> list) {
        if (list.size() == 0) return Collections.emptyList();
        ArrayList<Integer> result = new ArrayList<>();
        result.add(list.get(0));
        if (list.size() == 1) return result;
        for (int i = 1, listSize = list.size(); i < listSize; i++) {
            Integer integer = list.get(i);
            List<Integer> tail = list.subList(i + 1, Math.min(i + (i + 1), list.size()));
            int tailSum = tail.stream().mapToInt(Integer::intValue).sum();
            result.add(integer + tailSum);
        }
        return result;
    }

    void processSumAssert(List<Integer> inputList, List<Integer> expectedList) {
        List<Integer> result = processSum(inputList);
        assertThat(result).hasSize(inputList.size());
        assertThat(result).isEqualTo(expectedList);
    }

    @Test
    void processSumTests_8_elements() {
        processSumAssert(List.of(2, 5, 1, -9, 24, 3, 6, -8),
                List.of(2, 6, 16, 24, 25, 1, -2, -8));
    }

    @Test
    void processSumTests_1_element() {
        processSumAssert(List.of(2), List.of(2));
        processSumAssert(List.of(3), List.of(3));
    }

    @Test
    void processSumTests_1_other_element() {
        processSumAssert(Collections.emptyList(), Collections.emptyList());
    }

}