code: public static ErrorMessageFactory shouldContain(Object actual, Object expected, Object notFound) {
      return new ShouldContain(actual, expected, notFound);
    }
docs: Creates a new </code>{@link ShouldContain}</code>.
  @param actual the actual value in the failed assertion.
  @param expected values expected to be in {@code actual}.
  @param notFound the values in {@code expected} not found in {@code actual}.
  @return the created {@code ErrorMessageFactory}.