public int computeIfAbsent(final int key, final IntUnaryOperator mappingFunction)
    {
        requireNonNull(mappingFunction);
        final int missingValue = this.missingValue;
        final int[] entries = this.entries;
        @DoNotSub final int mask = entries.length - 1;
        @DoNotSub int index = Hashing.evenHash(key, mask);

        int value;
        while (missingValue != (value = entries[index + 1]))
        {
            if (key == entries[index])
            {
                break;
            }

            index = next(index, mask);
        }

        if (missingValue == value && missingValue != (value = mappingFunction.applyAsInt(key)))
        {
            entries[index] = key;
            entries[index + 1] = value;
            size++;
            increaseCapacity();
        }

        return value;
    }
@Test
    void shouldComputeIfAbsentUsingImplementation()
    {
        final Int2IntHashMap int2IntHashMap = new Int2IntHashMap(-1);
        final int key = 0;
        final int result = int2IntHashMap.computeIfAbsent(key, (k) -> k);
        assertEquals(key, result);
    }