### Question:
StringUtils { public static boolean isNullOrEmpty(String str) { return (str == null) || (str.isEmpty()); } private  StringUtils(); static boolean isNullOrEmpty(String str); static boolean isBlank(String str); static boolean isNotBlank(String str); static boolean equals(String a, String b); static boolean equalsIgnoreCase(String a, String b); static String inputStream2String(InputStream is); static byte[] inputStream2Bytes(InputStream is); static String toString(Object obj); static String trimToNull(final String str); static String trim(final String str); static boolean isEmpty(final CharSequence cs); static boolean isNotEmpty(final CharSequence cs); static final String EMPTY; }### Answer:
@Test public void testIsNullOrEmpty() { assertThat(StringUtils.isNullOrEmpty(null)).isTrue(); assertThat(StringUtils.isNullOrEmpty("abc")).isFalse(); assertThat(StringUtils.isNullOrEmpty("")).isTrue(); assertThat(StringUtils.isNullOrEmpty(" ")).isFalse(); }