### Question:
URLDecoderUtil { public static String decode(String sequence, String charset) { return UDecoder.URLDecode(sequence, charset); }  static String decode(String sequence, String charset); static String decode(String sequence, String charset, boolean isQueryString);  }### Answer:
@Test public void testURLDecodeStringInvalid() { Exception exception = null; try { URLDecoderUtil.decode("%5xxxxx", "ISO-8859-1"); } catch (Exception e) { exception = e; } assertTrue(exception instanceof IllegalArgumentException); exception = null; try { URLDecoderUtil.decode("%5", "ISO-8859-1"); } catch (Exception e) { exception = e; } assertTrue(exception instanceof IllegalArgumentException); }
@Test public void testURLDecodeStringValidIso88591Start() { String result = URLDecoderUtil.decode("%41xxxx", "ISO-8859-1"); assertEquals("Axxxx", result); }
@Test public void testURLDecodeStringValidIso88591Middle() { String result = URLDecoderUtil.decode("xx%41xx", "ISO-8859-1"); assertEquals("xxAxx", result); }
@Test public void testURLDecodeStringValidIso88591End() { String result = URLDecoderUtil.decode("xxxx%41", "ISO-8859-1"); assertEquals("xxxxA", result); }
@Test public void testURLDecodeStringValidUtf8Start() { String result = URLDecoderUtil.decode("%c3%aaxxxx", "UTF-8"); assertEquals("\u00eaxxxx", result); }
@Test public void testURLDecodeStringValidUtf8Middle() { String result = URLDecoderUtil.decode("xx%c3%aaxx", "UTF-8"); assertEquals("xx\u00eaxx", result); }
@Test public void testURLDecodeStringValidUtf8End() { String result = URLDecoderUtil.decode("xxxx%c3%aa", "UTF-8"); assertEquals("xxxx\u00ea", result); }
@Test public void testURLDecodePlusCharAsSpace() { String result = URLDecoderUtil.decode("a+b", "UTF-8", true); assertEquals("a b", result); }