void testJoinSingleNullElement() {
        String result = StringUtil.join(",", (CharSequence) null);
        assertEquals("null", result);
    }

    @Test
    @DisplayName("Should handle whitespace delimiter")
    void testJoinWithWhitespaceDelimiter() {
        String result = StringUtil.join("   ", "spaced", "out");
        assertEquals("spaced   out", result);
    }

    @Test

        assertNull(result, "getAnchorSet should return null for blank string");

        result = crawlerThread.getAnchorSet("   ");
        assertNull(result, "getAnchorSet should return null for whitespace string");
    }

    /**
     * Test getAnchorSet with list of URLs
     */
    @Test
    public void test_getAnchorSet_withList() {
        FessCrawlerThread crawlerThread = new FessCrawlerThread();

        while (st.hasMoreElements()) {
            list.add(st.nextElement().toString());
        }
        return list.toArray(new String[list.size()]);
    }

    /**
     * Removes whitespace from the left side of the string.
     *
     * @param text
     *            The text to trim
     * @return The resulting string
     */
    public static final String ltrim(final String text) {

      }
    }
  }

  /**
   * Reads the first line from a file. The line does not include line-termination characters, but
   * does include other leading and trailing whitespace.
   *
   * @param file the file to read from
   * @param charset the charset used to decode the input stream; see {@link StandardCharsets} for
   *     helpful predefined constants

        item.setNewInput(newSpecialInput);
        assertEquals(newSpecialInput, item.toLineString());
    }

    @Test
    public void test_whitespaceHandling() {
        // Test with various whitespace scenarios
        ProtwordsItem item1 = new ProtwordsItem(1, "  word  ");
        assertEquals("  word  ", item1.getInput());
        assertEquals("  word  ", item1.toLineString());

        assertEquals(emptyMessage, exception.getMessage());
        assertNull(exception.getCause());
    }

    @Test
    public void test_getMessage_withWhitespaceMessage() {
        // Test constructor with whitespace-only message
        String whitespaceMessage = "   ";
        SsoProcessException exception = new SsoProcessException(whitespaceMessage);

        assertEquals(whitespaceMessage, exception.getMessage());

import static com.google.common.base.CharMatcher.is;
import static com.google.common.base.CharMatcher.isNot;
import static com.google.common.base.CharMatcher.noneOf;
import static com.google.common.base.CharMatcher.whitespace;
import static com.google.common.truth.Truth.assertThat;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;

        ScriptEngine retrieved = scriptEngineFactory.getScriptEngine("test-engine.v1");
        assertNotNull(retrieved);
        assertEquals(engine, retrieved);
    }

    // Test add with whitespace in name
    @Test
    public void test_add_whitespaceInName() {
        TestScriptEngine engine = new TestScriptEngine();
        scriptEngineFactory.add("  test  ", engine);

        assertNotNull(result);
        assertTrue(result instanceof MatchAllQueryBuilder);
    }

    @Test
    public void test_execute_withWhitespaceContext() {
        // Test execute with whitespace query string context
        QueryContext context = new QueryContext("   ", false);
        MatchAllDocsQuery query = new MatchAllDocsQuery();
        float boost = 1.0f;

        // Blank fields are handled before Set lookup
        assertFalse(queryFieldConfig.isFacetField(""));
        assertFalse(queryFieldConfig.isFacetField(null));
        assertFalse(queryFieldConfig.isFacetField("   ")); // Whitespace only
    }

    /**
     * Test that updating fields via setter updates both array and Set.
     */
    @Test
    public void test_updateFields_updatesSetAndArray() {
        // Initial setup