### Question:
EnvvarSource extends PropertiesFormat implements ConfijSource { public static EnvvarSource withPrefix(String prefix) { return new EnvvarSource(prefix); } protected  EnvvarSource(String prefix); static EnvvarSource withPrefix(String prefix); @Override void override(ConfijNode rootNode);  }### Answer:
@Test void withPrefix() throws Exception { String value1 = UUID.randomUUID() + ""; String value2 = UUID.randomUUID() + ""; SystemLambda.withEnvironmentVariable("A_PREFIX_xy", value1) .and("A_PREFIX_others_fuu.", value2) .and("A_PREFIXORNORATALL_xy", "fuuuuu") .execute(() -> { Config config = ConfijBuilder.of(Config.class) .loadFrom("env:A_PREFIX") .build(); assertThat(config.xy()).isEqualTo(value1); assertThat(config.others()).containsExactly(new SimpleEntry<>("fuu.", value2)); }); }