public ResumableResult resume() {
            final ExecSessionInternal exec = newExecSessionInternal(this.resumeState.getExecSessionConfigSource());
            final ExecutionResult result;
            try {
                result = bulkLoader.resume(exec, config, resumeState);
            } catch (PartialExecutionException partial) {
                return new ResumableResult(partial);
            }
            return new ResumableResult(result);
        }
Sets an alternative {@code BulkLoader} instance mainly for testing-purpose.
embulk-core/src/main/java/org/embulk/EmbulkEmbed.java