code: public static ErrorMessageFactory shouldContainAtIndex(Object actual, Object expected, Index index, Object found) {
      return new ShouldContainAtIndex(actual, expected, index, found);
    }
docs: Creates a new </code>{@link ShouldContainAtIndex}</code>.
  
  @param actual the actual value in the failed assertion.
  @param expected value expected to be in {@code actual}.
  @param index the index of the expected value.
  @param found the value in {@code actual} stored under {@code index}.
  @return the created {@code ErrorMessageFactory}.