Simply Testable Blog

Figuring out how to automate away the pain of routine front-end web testing; the story behind

211 posts covering the initial idea, growth of the service, features, advances, failures and successes.

The goal all along of Simply Testable has been to let you easily run a set of frontend tests against any website of your choosing with the minimum possible effort.

Until recently you could only test a large subset of the Internet. It was a large subset of the Internet, but not the entirety.

For some sites you'd encounter a polite notice informing you that the given site is too large to be tested. For other sites your test would get stuck at "Finding URLs to test: looking for sitemap or news feed" and stay like that forever.

As of a few minutes ago, you can now test absolutely any website. Here is story of how we went from being able to test only a tiny subset of all websites to being able to test absolutely any website.

The Beginning: Simple Sitemaps Only

When the service first launched you could only run full-site tests for sites with simple sitemaps.

Collecting URLs to test from a sitemap is much easier than crawling a site to find URLs. And simple sitemaps are much easier to collect and process than compressed sitemaps, indexed sitemaps and multiple sitemaps.

There was a whole range of sites you couldn't test but it was better than nothing and allowed me to focus on building a great testing tool instead of building a great sitemap reading tool.

The private alpha was released on September 12, 2012 and all was good. Limited, covering only a small subset of the Internet and offering just the one feature, but good.

News Feed (RSS, Atom) Support

Some sites have no sitemap but do publish news feeds, either in RSS or Atom format. And some such sites have been around since the dawn of time and if they haven't added a sitemap yet they may well never do.

Whereas a sitemap will ideally list all URLs, a news feed will typically list a subset of all URLs and commonly these will be the most recent. This turns out to be a good substitute for a sitemap.

On September 19, 2012, support for news feeds was mentioned in the weekly newsletter and so support for this was probably added around then.

Millions of WordPress blogs and Blogger sites could now be tested.

Compressed Sitemaps

Instead of serving an XML document listing URLs and metadata about those URLs, some people take their XML sitemap and gzip it and serve the gzipped archive.

Who'd have thought it? Well, anyone who has read the offical spec might have thought of it, that's who.

In relation to sitemap size, the spec states:

If you would like, you may compress your Sitemap files using gzip to reduce your bandwidth requirement …

On September 21, 2012, support for compressed sitemaps was added and the small subset of the Internet that could be tested grew a little.

Multiple Sitemaps and Indexed Sitemaps

On the subject of sitemap size, the spec states:

You can provide multiple Sitemap files, but each Sitemap file that you provide must have no more than 50,000 URLs and must be no larger than 10MB (10,485,760 bytes). … If you want to list more than 50,000 URLs, you must create multiple Sitemap files.

Some sites have more than 50,000 URLs. The staff of some have stalled at the stage of trying to manually count the number of URLs to verify the situation for management so we'll ignore them for now.

At this point in time we supported only single, simple sitemaps. If your sitemap was an index that listed other sitemaps you were out of luck. And if you listed many sitemaps in your robots.txt you were out of luck.

On October 10, 2012, just nipping in prior to the public launch, support for multiple sitemaps and indexed sitemaps was added.

As an aside as an implementor of a tool that discovers and retrieves sitemaps, I'd like to point out the range of sitemap combinations that you as a site owner could opt for:

  • a single simple sitemap (listed either in robots.txt or just floating around hoping to get noticed)

  • a single simple sitemap index providing URLs to your actual sitemaps (listed either in robots.txt or just floating around hoping to get noticed)

  • multiple simple sitemaps listed in robots.txt

  • multiple simple sitemaps indexes listed in robots.txt, each listing URLs to your actual sitemaps

  • multiple sitemaps listed in robots.txt, some simple sitemaps and some indexes to other sitemaps, in any combination you fancy

With support for multiple sitemaps and indexed sitemaps added, you could opt for any of the above.

Crawling To Discover URLs

All of the above changes allowed the subset of the Internet that could be tested to expand quite a bit but it still failed to cover a notable portion of the Internet: sites with no sitemap and no news feed that will never have a sitemap or news feed.

I knew from the start that there would always be some sites that had no sitemap and no news feed. It wasn't possible to discover URLs to test and so such sites couldn't be tested.

This might seem like a problem, but when you have to choose between improving support for sites that can be tested and improving the breadth of sites that can be tested, it's only a problem if the number of sites that can't be tested is significant.

Armed with a database of past results and the power of SQL, I set about the task of finding out. In 0.0002 seconds I had my answer: about 70% of tests failed due to there being no sitemap and no news feed.

7 out of every 10 full-site tests that were attempted couldn't happen due to there being no sitemap and no news feed. Even with my limited understanding of statistical analysis I could tell that 70% is significant.

On August 22, 2013 I announced the new site crawler that would walk all over your site finding URLs to test.

I boldly stated at the time that:

There is now no site that we cannot test.

I was wrong about this but didn't realise it at the time. I thought I was telling the truth.

There is now no site that we cannot test. And I mean it this time.

Back when I last claimed that there was no site we cannot test I was wrong but not by much.

Sites that have sitemaps provided in an array of possible ways could be tested. Sites with news feeds could be tested. And sites without sitemaps and without news feeds could be tested.

What was missing was the ability to test sites that did have sitemaps but where on a scale of 1 to 10 regarding the size of the sitemap they rated somewhere around 27.

One thing I quickly spotted after the public launch was that sites with insanely large sitemaps caused problems.

The background process that was kicked off to collect the sitemap for a site with an insanely large sitemap would take quite a while going about it, consuming more and more server resources as it went. Over time, this would approximate to consuming all server resources and bring things to a grinding halt. All things.

As a quick and messy fix to the problem of the production server breaking in style every now and again without warning, I scheduled a job to run every few minutes that would kill any sitemap-gathering process that had been running for longer than 2 minutes.

The fix was quick and messy but allowed me to do anything other than keep a constant eye on the production server. That was good enough for me and let me get on with anything else.

This did mean that there was still a small subset of the Internet that could not be tested. And if you tried to test one of such sites, you test would get stuck at "Finding URLs to test: looking for sitemap or news feed" and stay like that forever. This is not a good experience.

This week I set about sorting out this mess once and for all.

Handling Sites With Insanely Large Sitemaps

I was examining a particular site earlier this week. It had a very large sitemap. "How large is large?", I hear you ask.

The site I was examining had a single index listing 1396 sitemaps, each listing about 8,000 URLs. That's about 11 million URLs.

This particular site also had an interesting property: it was very slow. When a slow site serves a single web page it may take some seconds longer than you expect.

When a slow site is so slow that it times out serving a single sitemap and when the site has 1396 sitemaps to give you, you end up waiting around a long time.

Each request to retrieve each sitemap is given 30 seconds to go about it. This is more than enough time for the majority of sites and includes plenty of waiting time for any regularly-slow site.

But for a site with 1396 sitemaps each timing out after 30 seconds, you have to wait 1396 * 30 seconds to finish the process of retrieving the full sitemap from which to gather URLs to be tested.

1396 * 30 seconds might sound like a while but it's hard to fully appreciate as we don't normally encounter large amounts of seconds. It seems long, but how long? It's about 11 hours, that's how long.

Even if the production server didn't have a background process that periodically killed off long-running processes that were stuck collecting sitemaps, I can't imagine you'd sit around waiting 11 hours for your test to start. Personally, I'd definitely give up after 5 hours.

The ability to specify a timeout value for a HTTP request is pretty universal and certainly available to, and most likely used by, any application that uses cURL in the background to handle HTTP communication.

In this case that wasn't helping. I could reduce the timeout per HTTP request from 30 seconds to 1 second. I'd then only have to wait about 20 minutes to fail to retrieve a very large collection of sitemaps.

Well, that's not going to work. 20 minutes is still about 19 minutes longer than I'd like. And then there would be a problem with regularly-slow sites that spent a whole 2 seconds to serve up their sitemaps.

I then hit upon the so-obvious-why-didn't-I-think-of-it-before solution of specifying a timeout to be applied to a collection of HTTP requests instead of just one.


Every site now has a full 60 seconds for the full sitemap to be retrieved. It your site has 1396 large sitemaps and isn't slow and serves them up at a rate of 1 per second, the first 60 would be retrieved and the rest would be ignored.

Not all the URLs of such a site would be discovered, but a lot would, certainly enough to give you a good idea of the overall quality of your site once all the tests you selected had finished.

There is now definitely no site that cannot be tested. Updates will follow as soon as I found out that this is not true.