### Question:
CaseTools { public static String lcase(String s) { return xcase(s, Character::toLowerCase); }  static String lcase(String s); static String ucase(String s); static String camel(String s); static String snake(String s);  }### Answer:
@Test @DisplayName("lcase converts properly normal not empty string that starst with a letter") void lcaseConverts() { assertEquals("abc", lcase("Abc")); }
@Test @DisplayName("lcase converts properly empty string") void lcaseConvertsZeroLengthString() { assertEquals("", lcase("")); }
@Test @DisplayName("lcase converts properly null string") void lcaseConvertsNull() { assertNull(null, lcase(null)); }