### Question:
ConfigMappers { static Map<Class<?>, Function<Config, ?>> essentialMappers() { return ESSENTIAL_MAPPERS; } private  ConfigMappers(); static Byte toByte(String stringValue); static Short toShort(String stringValue); static Integer toInt(String stringValue); static Long toLong(String stringValue); static Float toFloat(String stringValue); static Double toDouble(String stringValue); static Boolean toBoolean(String stringValue); static Character toChar(String stringValue); static Class<?> toClass(String stringValue); static UUID toUUID(String stringValue); static BigDecimal toBigDecimal(String stringValue); static BigInteger toBigInteger(String stringValue); static File toFile(String stringValue); static Path toPath(String stringValue); static Charset toCharset(String stringValue); static Pattern toPattern(String stringValue); static URI toUri(String stringValue); static URL toUrl(String stringValue); @SuppressWarnings({"UseOfObsoleteDateTimeApi", "DeprecatedIsStillUsed"}) @Deprecated static Date toDate(String stringValue); @SuppressWarnings({"UseOfObsoleteDateTimeApi", "DeprecatedIsStillUsed"}) @Deprecated static Calendar toCalendar(String stringValue); @SuppressWarnings({"UseOfObsoleteDateTimeApi", "DeprecatedIsStillUsed"}) @Deprecated static GregorianCalendar toGregorianCalendar(String stringValue); static LocalDate toLocalDate(String stringValue); static LocalTime toLocalTime(String stringValue); static LocalDateTime toLocalDateTime(String stringValue); static ZonedDateTime toZonedDateTime(String stringValue); static ZoneId toZoneId(String stringValue); static ZoneOffset toZoneOffset(String stringValue); @SuppressWarnings({"UseOfObsoleteDateTimeApi", "DeprecatedIsStillUsed"}) @Deprecated static TimeZone toTimeZone(String stringValue); @SuppressWarnings({"UseOfObsoleteDateTimeApi", "DeprecatedIsStillUsed"}) @Deprecated static SimpleTimeZone toSimpleTimeZone(String stringValue); static Instant toInstant(String stringValue); static OffsetDateTime toOffsetDateTime(String stringValue); static OffsetTime toOffsetTime(String stringValue); static Duration toDuration(String stringValue); static Period toPeriod(String stringValue); static Map<String, String> toMap(Config config); static Properties toProperties(Config config);  }### Answer:
@Test public void testEssentialMappers() { ConfigMapperManager manager = BuilderImpl.buildMappers(ConfigMapperManager.MapperProviders.create()); Config config = Config.builder() .sources(ConfigSources.create(Map.of( "text-text", "string value", "int-p", "2147483647", "long-p", "9223372036854775807", "double-p", "1234.5678"))) .build(); assertThat(manager.map(config, Config.class), is(config)); assertThat(manager.map(config.get("text-text"), String.class), is("string value")); assertThat(manager.map(config.get("int-p"), OptionalInt.class).getAsInt(), is(2147483647)); assertThat(manager.map(config.get("long-p"), OptionalLong.class).getAsLong(), is(9223372036854775807L)); assertThat(manager.map(config.get("double-p"), OptionalDouble.class).getAsDouble(), is(1234.5678)); }