public OutputBuilder inputSchema(SchemaConfig inputSchema) {
            if (inputSchema == null) {
                throw new NullPointerException("inputSchema");
            }
            this.inputSchema = inputSchema;
            return this;
        }
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