private ConfigSource newParserConfig() {
            return newConfig()
                    .set("charset", "UTF-8")
                    .set("newline", "LF")
                    .set("type", "csv")
                    .set("delimiter", ",")
                    .set("quote", "\"")
                    .set("escape", "\"")
                    .set("skip_header_lines", 1)  // Skip the header because the input csv must have "columnName:columnType" defined in the header.
                    .set("columns", newSchemaConfig());
        }
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