How to test PUT method using supertest and jasmine - node

I am creating an API with expressjs and my routes look like this:

module.exports = function(app){
var book = require('../controllers/book.controller');

app.get('/api/books', book.getBooks); //get all books
app.post('/api/books', book.addBook); //add a book
app.put('/api/book/:book_id', book.updateBook); //update a book entry
app.delete('/api/book/:book_id', book.deleteBook); //delete a book
}

      

        
        
        
      

    

Callback functions are defined as follows

var Book = require('../models/book.model');

module.exports = {
  addBook: function(req, res){
    Book.create(req.body, function(err, book){
      if(err){
        return res.json(400, err);
      }
      res.status(201).json(book);
    });
  },

  getBooks: function(req, res){
    Book.find({}).exec(function(err, books){
      if(err){
        return res.json(400, err);
      }
      res.status(201).json(books);
    });
  },

  getOneBook: function(req, res){
    Book.findById({_id: req.params.book_id}, function(err, book){
      if(error){
        return res.json(400, err)
      }
      res.status(201).json(book);
    })
  },

  updateBook: function(req, res){
    Book.update({_id: req.params.book_id}, req.body, function(err, book){
      if(err){
        return res.json(400, err);
      }
      res.status(201).json(book);
    });
  },

  deleteBook: function(req, res){
    Book.remove({_id: req.params.book_id}, function(err, book){
      if(err){
        return res.json(400, err);
      }
      res.status(200).json(book);
    })
  }
};

      

        
        
        
      

    

I am testing routes with jasmine - node and supertest and this is what I have done so far

var app = require('../app.js');
var request = require('supertest')(app);

describe('Test for book route', function(){

  it('Test GET method for /api/books', function(done){
    request
    .get('/api/books')
    .expect(201)
    .expect('Content-Type', 'application/json; charset=utf-8')
    .end(function(err, res){
      if(err){
        return done(err);
      }
      done();
    });
  });

  it('Test POST method for /api/books', function(done){
    var book = {title: 'Ake', author: 'Wole Soyinka', blurb: 'An autobiography'};
    request
      .post('api/books')
      .send(book)
      .expect(200)
      done();
  });
//THIS IS WHERE THE ISSUE IS
  it('Test PUT method for /api/book/:book_id', function(done){
    var bookEdit = {title: 'Ake', author: 'Wole Soyinka', blurb: 'An autobiography by the only Nigerian Nobel Laureate'};
    request
      .put('api/book/:book_id')
      .send(bookEdit)
      .expect(200)
      .done();
  });

});

      

        
        
        
      

    

What is the best way to get the book_id variable so that I can edit the post created with the PUT test?