StopwordsItem item1 = new StopwordsItem(1, "test");
        StopwordsItem item2 = new StopwordsItem(1, "test");

        item1.setNewInput("updated");
        item2.setNewInput("different");

        // Should still be equal based on original input
        assertTrue(item1.equals(item2));
    }

    @Test
    public void test_equals_withNullInput() {

        CharMappingItem item2 = new CharMappingItem(2L, inputs2, "output");
        CharMappingItem item3 = new CharMappingItem(3L, inputs3, "output");
        CharMappingItem item4 = new CharMappingItem(4L, inputs1, "different");

        // Same inputs and output should have same hash code
        assertEquals(item1.hashCode(), item2.hashCode());

        // Symmetry
        assertTrue(item1.equals(item2));
        assertTrue(item2.equals(item1));
    }

    @Test
    public void test_equals_withNullInput() {
        // Test equals with null input - should not throw, uses null-safe comparison
        ProtwordsItem item1 = new ProtwordsItem(1, null);
        ProtwordsItem item2 = new ProtwordsItem(2, null);

        String[] text2 = { "item2" }; // Different text -> different ID
        String[][] readings2 = { { "read2" } };
        SuggestItem item2 = new SuggestItem(text2, readings2, null, 0L, 0L, 1.0f, null, null, null, SuggestItem.Kind.QUERY);

        SuggestItem.merge(item1, item2); // Should throw IllegalArgumentException
    }

        Map<String, Object> dataMap = new HashMap<>();

        // Add a List as initial value
        List<String> initialList = new ArrayList<>();
        initialList.add("item1");
        initialList.add("item2");
        dataMap.put("items", initialList);

        // Add a new value
        transformer.putResultDataBody(dataMap, "items", "item3");

        Object result = dataMap.get("items");

        readings2[0] = new String[] { "next" };
        SuggestItem item2 = new SuggestItem(new String[] { "次" }, readings2, new String[] { "content" }, 1, 0, -1, new String[] { "tag1" },
                new String[] { SuggestConstants.DEFAULT_ROLE }, null, SuggestItem.Kind.DOCUMENT);
        suggester.indexer().index(item2);
        suggester.refresh();

        OptionalEntity<CharMappingItem> result2 = charMappingFile.get(2L);
        assertTrue(result2.isPresent());
        CharMappingItem item2 = result2.get();
        assertEquals(2L, item2.getId());
        assertArrayEquals(new String[] { "d", "e" }, item2.getInputs());
        assertEquals("f", item2.getOutput());

        OptionalEntity<CharMappingItem> result3 = charMappingFile.get(3L);
        assertFalse(result3.isPresent());
    }

        String[] text2 = { "test" };
        String[][] readings2 = { { "test" } };
        SuggestItem item2 = new SuggestItem(text2, readings2, null, 5L, 10L, 1.0f, new String[0], null, null, SuggestItem.Kind.QUERY);

        SuggestItem merged = SuggestItem.merge(item1, item2);

        assertNotNull(merged);
        assertEquals(30L, merged.getQueryFreq());
        assertEquals(15L, merged.getDocFreq());

        SuggestItem item2 = new SuggestItem(new String[] { "テスト" }, readings, new String[] { "content" }, 2, 0, -1, new String[] { "tag2" },
                new String[] { SuggestConstants.DEFAULT_ROLE }, null, SuggestItem.Kind.DOCUMENT);

        SuggestItem[] mergedItems = writer.mergeItems(new SuggestItem[] { item1, item2 });

        assertNotNull(mergedItems);

    }

    /**
     * Merges two suggest items.
     * @param item1 The first suggest item.
     * @param item2 The second suggest item.
     * @return The merged suggest item.
     */
    public static SuggestItem merge(final SuggestItem item1, final SuggestItem item2) {
        return SuggestItemMerger.merge(item1, item2);
    }

    /**
     * Checks if the suggest item contains any of the given bad words.