private static Set<String> readPropertyKeys(final String name) {
        try (final InputStream in = EmbulkEmbed.class.getResourceAsStream(name)) {
            if (in == null) {
                throw new NullPointerException(
                        String.format("Resource '%s' is not found in classpath. Jar file or classloader is broken.", name));
            }
            final Properties properties = new Properties();
            properties.load(in);
            return Collections.unmodifiableSet(properties.stringPropertyNames());
        } catch (final IOException ex) {
            logger.error("Failed to read a resource :" + name + ". Ingored.", ex);
            return Collections.unmodifiableSet(new HashSet<>());
        }
    }
Sets an alternative {@code BulkLoader} instance mainly for testing-purpose.
embulk-core/src/main/java/org/embulk/EmbulkEmbed.java