### Question:
StringUtils { @SuppressWarnings("StringEquality") public static boolean isEqual(String s1, String s2) { if (s1 == null || s2 == null) { return s1 == s2; } return s1.equals(s2); }  @SuppressWarnings("StringEquality") static boolean isEqual(String s1, String s2);  }### Answer:
@Test public void isEqual() throws Exception { assertThat(StringUtils.isEqual(null, "a")).isFalse(); assertThat(StringUtils.isEqual("a", null)).isFalse(); assertThat(StringUtils.isEqual("a", "b")).isFalse(); assertThat(StringUtils.isEqual("a", "A")).isFalse(); assertThat(StringUtils.isEqual("a", "a")).isTrue(); assertThat(StringUtils.isEqual("", "")).isTrue(); }