check the size of a downloaded file in a test using webdriverio and superagent

download-file-test.js

var should = require("chai").should();
var request = require("superagent");

var page = {
	url: "http://saucelabs.github.io/training-test-page/",
	title: "I am a page title - Sauce Labs",
	logo: { selector: "img:first-of-type", filename: "saucelogo.png", size: 9666 }
};

describe("download file", function() {

	it("should be the right size", function() {

		// use webdriverio to get the url of the file to download
		browser.url(page.url);
		var title = browser.getTitle();
		title.should.equal(page.title);

		var logo_url = browser.getAttribute(page.logo.selector, "src");
		logo_url.should.contain(page.logo.filename);

		// use superagent to download and verify the file size
		
		// you can check the content length without actually downloading the file with a HEAD request
		request.head(logo_url).end(function(error, response) {
			var contentLength = parseInt(response.headers["content-length"]);
			contentLength.should.equal(page.logo.size);
		})

		// you can also download the full file contents to inspect with a GET request
		request.get(logo_url).end(function(error, response) {
			var contentLength = parseInt(response.headers["content-length"]);
			var size = response.body.length;
			contentLength.should.equal(size);
		})
	});
});