### Question:
StringToInstantConverter implements Converter<String, Instant> { @Override public Instant convert(@NonNull String source) { TemporalAccessor parsed = PARSER.parse(source); return Instant.from(parsed); }  @Override Instant convert(@NonNull String source);  }### Answer:
@Test void should_convert_string_to_instant() { var input = "20190101123456789"; var expected = Instant.parse("2019-01-01T12:34:56.789Z"); StringToInstantConverter converter = new StringToInstantConverter(); Instant actual = converter.convert(input); assertThat(actual).isEqualTo(expected); }