Nodejs = ReferenceError: getReadableStreamSomehow is not defined

I try to implement stream in my node app but i getting "getReadableStreamSomehow is not defined" error so how can i solve this error?

My code like this

const readable = getReadableStreamSomehow();
const writable = fs.createWriteStream('file.txt');
// All the data from readable goes into 'file.txt'
readable.pipe(writable);

via test