### Question:
StringUtils { public static String dotToDash(String input) throws IllegalArgumentException { if (input == null) throw new IllegalArgumentException("dotToDash argument must not be null"); return input.replaceAll("\\.", "-"); }  static String arrayFormat(String format, Object[] items); static Optional<String> cdr(String name, String... sep); static String car(String name, String... sep); static String lastOf(String qualifiedName, String... sep); static String untill(String qualifiedName, String... sep); static String dotToUpperCamelCase(String input); static String dotToDash(String input); static String camelCaseToDash(String input); static boolean isPackageFriendly(String moduleName); static String withoutTypeArgs(String javaTypeString); static String notEmptytrimmed(String param); static Optional<Tuple<String, String>> splitIntoTwo(String mappingString); static int countMatches(String theString, String... sep);  }### Answer:
@Test void testdotDash_Fail() { assertThrows(IllegalArgumentException.class, () -> dotToDash(null) ); }
@Test void testDotToDash() { assertEquals("",dotToDash("")); assertEquals("a-b",dotToDash("a.b")); assertEquals("a-b-c",dotToDash("a.b.c")); }