### Question:
SmallRyeConfig implements Config, Serializable { @Deprecated public void addConfigSource(ConfigSource configSource) { configSources.updateAndGet(configSources -> new ConfigSources(configSources, configSource)); } SmallRyeConfig(SmallRyeConfigBuilder builder, ConfigMappings mappings); @Deprecated protected  SmallRyeConfig(List<ConfigSource> configSources, Map<Type, Converter<?>> converters); C getValues(String name, Class<T> itemClass, IntFunction<C> collectionFactory); C getValues(String name, Converter<T> converter, IntFunction<C> collectionFactory); @Override T getValue(String name, Class<T> aClass); @SuppressWarnings("unchecked") T getValue(String name, Converter<T> converter); boolean rawValueEquals(String name, String expected); @Experimental("Extension to the original ConfigSource to allow retrieval of additional metadata on config lookup") ConfigValue getConfigValue(String name); String getRawValue(String name); @Override Optional<T> getOptionalValue(String name, Class<T> aClass); Optional<T> getOptionalValue(String name, Converter<T> converter); Optional<C> getOptionalValues(String name, Class<T> itemClass,
            IntFunction<C> collectionFactory); Optional<C> getOptionalValues(String name, Converter<T> converter,
            IntFunction<C> collectionFactory); ConfigMappings getConfigMappings(); @Experimental("ConfigMapping API to group configuration properties") T getConfigMapping(Class<T> type); @Experimental("ConfigMapping API to group configuration properties") T getConfigMapping(Class<T> type, String prefix); @Override Iterable<String> getPropertyNames(); @Override Iterable<ConfigSource> getConfigSources(); @Deprecated void addConfigSource(ConfigSource configSource); T convert(String value, Class<T> asType); @SuppressWarnings("unchecked") Converter<T> getConverter(Class<T> asType);  }### Answer:
@Test void addConfigSource() { SmallRyeConfig config = new SmallRyeConfigBuilder().addDefaultSources().addDefaultInterceptors().build(); assertNull(config.getConfigValue("my.prop").getValue()); config.addConfigSource(config("my.prop", "1")); assertEquals("1", config.getRawValue("my.prop")); }