javascript - Mocha tests for fs.readFile -

my server code has simple route in need send tiny thumbnail (jpeg) client display. here's sample of code:

router.get('/thumbnail/:title/',function(req,resp){     let title = req.params.title;      getfilename(title).then(thumbnailcb,errorcb);      function thumbnailcb(jpeg){         fs.readfile(jpegfile,sendjpegfile);     }      function sendjpegfile(err,data){         if ( err ) {             fs.readfile(default_thumbnail,senddefault);         } else {             resp.send(data);         }     };      function senddefault(err,data){         if ( err ) {console.log(err);}          else { resp.send(data); }     };      function errorcb(error){         console.log(error);     }; }); 

i trying test in mocha. first thought compare buffers, , apparently, not 1 think this: https://github.com/mochajs/mocha/issues/1624

so, not working. following mocha/chai code. mocha hangs on assert call. have suggestions on testing route?

it('should thumbnail title',function(done){     const default_thumbnail = /* default file */;     const titlenotfound = /* random title */;      request(app)     .get(url + '/thumbnail/' + titlenotfound)     .expect(200)     .expect('content-type','application/octet-stream')     .end(function(err,res){         fs.readfile(default_thumbnail,'utf-8',function(err,data){             if(err){done(err);}             assert(data.tostring(),res.text.tostring()); // no bueno             done();         });     }); });