public class ErrorMessageHelper {

    @Autowired
    private MessageSource messageSource;

...
}

@Configuration
public class AppConfig {
    protected final Log logger = LogFactory.getLog(getClass());

    @Bean
    public static PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {
        PropertySourcesPlaceholderConfigurer configurer = new PropertySourcesPlaceholderConfigurer();
        return configurer;
    }
    
    @Bean
    public MessageSource messageSource() {
        ReloadableResourceBundleMessageSource messageSource = new ReloadableResourceBundleMessageSource();
        messageSource.setUseCodeAsDefaultMessage(true);
        messageSource.setDefaultEncoding("UTF-8");
        messageSource.setBasename("errors");
        messageSource.setCacheSeconds(0);
        return messageSource;
    }
    
}

@Configuration
@PropertySources({
    @PropertySource(value = "classpath:test.properties", ignoreResourceNotFound = false)
})
public class AppConfigTest {

    protected final Log logger = LogFactory.getLog(getClass());

    @Bean
    public static PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {
        PropertySourcesPlaceholderConfigurer configurer = new PropertySourcesPlaceholderConfigurer();
        return configurer;
    }



    @Bean
    public ErrorMessageHelper errorMessageHelper() {
        return new ErrorMessageHelper();
    }

}