public RunResult runInput(ConfigSource inConfig, Path outputPath) throws IOException {
        return inputBuilder()
                .in(inConfig)
                .outputPath(outputPath)
                .run();
    }
This method returns PreviewResult.

@return PreviewResult returns the result by PreviewExecutor
@throws IOException in case of failures in file operations
embulk-junit4/src/main/java/org/embulk/test/TestingEmbulk.java