How to write tests for web crawler?

I would like to learn how to write tests for applications in Node.js - in this example webcrawler.

Example code:

var request = require('request');
var cheerio = require('cheerio');
var URL = require('url-parse');

var START_URL = "http://ift.tt/nYiyza";
var SEARCH_WORD = "stemming";
var MAX_PAGES_TO_VISIT = 10;

var pagesVisited = {};
var numPagesVisited = 0;
var pagesToVisit = [];
var url = new URL(START_URL);
var baseUrl = url.protocol + "//" + url.hostname;

pagesToVisit.push(START_URL);
crawl();

function crawl() {
  if(numPagesVisited >= MAX_PAGES_TO_VISIT) {
    console.log("Reached max limit of number of pages to visit.");
    return;
  }
  var nextPage = pagesToVisit.pop();
  if (nextPage in pagesVisited) {
    // We've already visited this page, so repeat the crawl
    crawl();
  } else {
    // New page we haven't visited
    visitPage(nextPage, crawl);
  }
}

function visitPage(url, callback) {
  // Add page to our set
  pagesVisited[url] = true;
  numPagesVisited++;

  // Make the request
  console.log("Visiting page " + url);
  request(url, function(error, response, body) {
     // Check status code (200 is HTTP OK)
     console.log("Status code: " + response.statusCode);
     if(response.statusCode !== 200) {
       callback();
       return;
     }
     // Parse the document body
     var $ = cheerio.load(body);
     var isWordFound = searchForWord($, SEARCH_WORD);
     if(isWordFound) {
       console.log('Word ' + SEARCH_WORD + ' found at page ' + url);
     } else {
       collectInternalLinks($);
       // In this short program, our callback is just calling crawl()
       callback();
     }
  });
}

function searchForWord($, word) {
  var bodyText = $('html > body').text().toLowerCase();
  return(bodyText.indexOf(word.toLowerCase()) !== -1);
}

function collectInternalLinks($) {
    var relativeLinks = $("a[href^='/']");
    console.log("Found " + relativeLinks.length + " relative links on page");
    relativeLinks.each(function() {
        pagesToVisit.push(baseUrl + $(this).attr('href'));
    });
}

So... How to test such code? I know I should share applications for small portions, but in this case it makes no sense. Is there one general test for this application that gives sample data and then checks if it returns what we expect? What else can we test here?

I can use Mocha, Expect or others...