### Question:
StringUtils { public static boolean isNullOrEmpty(final String str) { return null == str || str.isEmpty(); } private  StringUtils(); static boolean isNullOrEmpty(final String str); static boolean isNullOrWhitespace(final String str); static String replaceVariable(final String string, final String name, final String value); static boolean equalsIgnoreCase(
      Optional<String> optionalString1, Optional<String> optionalString2);  }### Answer:
@Test public void isNullOrEmptyReturnsCorrectResult() { MatcherAssert.assertThat(StringUtils.isNullOrEmpty(null), IsEqual.equalTo(true)); MatcherAssert.assertThat(StringUtils.isNullOrEmpty(""), IsEqual.equalTo(true)); MatcherAssert.assertThat(StringUtils.isNullOrEmpty(" "), IsEqual.equalTo(false)); MatcherAssert.assertThat(StringUtils.isNullOrEmpty(" \t \t"), IsEqual.equalTo(false)); MatcherAssert.assertThat(StringUtils.isNullOrEmpty("foo"), IsEqual.equalTo(false)); MatcherAssert.assertThat(StringUtils.isNullOrEmpty(" foo "), IsEqual.equalTo(false)); }