...

class StringUtilTest {

    @Test
    @DisplayName("Should join single element without delimiter")
    void testJoinSingleElement() {
        String result = StringUtil.join(",", "hello");
        assertEquals("hello", result);
    }

    @Test
    @DisplayName("Should join two elements with delimiter")
    void testJoinTwoElements() {
        String result = StringUtil.join(",", "hello", "world");

                return StringUtils.join(newInputs, ",");
            }
            return StringUtils.join(newInputs, ",") + "=>" + StringUtils.join(newOutputs, ",");
        }
        if (Arrays.equals(inputs, outputs)) {
            return StringUtils.join(inputs, ",");
        }
        return StringUtils.join(inputs, ",") + "=>" + StringUtils.join(outputs, ",");
    }

     *
     * @return compact string representation of the mapping rule
     */
    public String toLineString() {
        if (isUpdated()) {
            return StringUtils.join(newInputs, ",") + "=>" + newOutput;
        }
        return StringUtils.join(inputs, ",") + "=>" + output;
    }

     */
    private StringUtil() {
    }

    /**
     * Implementation of {@link java.lang.String#join} backported for JDK7.
     *
     * @param delimiter the separator to use between elements
     * @param elements the elements to join
     * @return elements separated by delimiter
     */
    public static String join(final CharSequence delimiter, final CharSequence... elements) {
        final StringBuilder sb = new StringBuilder();

    }

    /**
     * Joins array or list elements into a single space-separated string.
     *
     * @param input the input object (String[], List, or String)
     * @return joined string with elements separated by spaces, or empty string if invalid input
     */
    public static String join(final Object input) {
        String[] values = null;

                }
            });
        }

        for (Thread th : threads) {
            th.start();
        }
        for (Thread th : threads) {
            th.join();
        }
        assertEquals(num, count.get());
        assertEquals(num, valueSet.size());

        Set<String> valueSet2 = Collections.synchronizedSet(new HashSet<>());
        threads = new Thread[threadNum];

        }
        for (int i = 0; i < crawlerContext.numOfThread; i++) {
            threads[i].start();
        }

        // join
        for (int i = 0; i < crawlerContext.numOfThread; i++) {
            try {
                threads[i].join();
            } catch (final InterruptedException e) {

        for (final String key : extractData.getKeySet()) {
            logger.info("{}={}", key, String.join("|", extractData.getValues(key)));
        }
        assertEquals("4", extractData.getValues("cp:revision")[0]);
        assertEquals("こめんと", extractData.getValues("w:Comments")[0]);
        assertEquals("たぐ|さぶたいとる", String.join("|", extractData.getValues("dc:subject")));

     *
     * @return The stopword as a string.
     */
    public String toLineString() {
        if (isUpdated()) {
            return StringUtils.join(newInput);
        }
        return StringUtils.join(input);
    }